3.5e's big attempt came in the form of Teamwork Benefits, which were sort of like "feats" for your party. A team was two-to-eight intelligent creatures (though animal companions with the "teamwork" trick could also count) and your team had one teamwork benefit slot per 4 HD of the lowest-HD member of the team. The definition of team definitely approached "grandfather's axe" levels since you could replace missing team-mates with two weeks of training to get into the swing of the group's style. Oddly enough, it was easy enough to get around the teamwork limitation if you Wolverine'd yourself out into several different teams at the same time, or even the same team members counting as several different teams each with their own benefits, though you did have to train for four weeks per year to maintain the team benefit (but the weeks didn't have to be consecutive).
Anyways, Teamwork benefits functioned sort of like feats in that they each had a prerequisite that you needed to meet, but there was a greater prerequisite for the team leader and then a lesser prerequisite for individual team members (so you might need 8 ranks of Hide/Move Silently to be a stealth team leader, but only one rank to be a member). Team leaders also needed an Intelligence of 8 or higher, so no letting your dog lead. You always needed at least one member who met the prereqs for leader in order to use the teamwork ability, though you could have up to seven members so long as they met the member prerequisites.
So, what sort of benefits could you get from working together? Well, not murdering each other as hard, for one. There were benefits to grant all members of your team the ability to dodge AoE spells from friendly targets as if using evasion, as well as reduce the penalty for firing into melee or enemies gaining cover from your allies, but you could also boost things like morale checks. There were some oddly-specific benefits such as one that was only worthwhile if everyone in the team was part of a cavalry unit, or if your party had a specific urge to break grapples, make bull rushes to push foes, or use battering rams, but there were also generically useful ones such as the ability to pile into a flank, spam spells to lower subsequent Reflex saves, travel at full speed while being stealthy or make free Spot/Listen checks each round. There was even the teamwork ability that allowed you to throw yourself in front of attacks aimed at your glorious casting masters (though it was only for attacks provoked by casting, which most casters stopped provoking by mid levels) or slap your allies out of mind-control effects. Less useful were the oddly-specific ones such as one focused on listening at doorways or the one that let your allies automatically stabilize dying creatures, but only if one ally had already failed to do so this round- two allies wasting their turn not doing something important isn't all that hot in a game of skill check boosters and healing magic.
Still, it's a free boost your capabilities, which isn't all that bad. The DMG II also introduced rules for a companion spirit, which required party members to invest gold and XP to benefit from a shared magical ability- and this one at least limited you to one companion spirit per person (though the same spirit could be shared by up to eight members). Some interesting options, but let's move on.
Over in Pathfinder, they seem to have taken inspiration from the 3e Teamwork Benefits and introduced the concept of Teamwork Feats. Unlike Teamwork Benefits, Teamwork Feats are actual feats which you take that work under certain circumstances if one or more allies also has the same feat. Unfortunately, while most of the time building a character just involves picking up things that are interesting to you, Teamwork feats require you to not only figure out which ones are interesting enough to purchase with your precious feat slots, but are interesting enough to convince as many of your team members as possible to buy in as well. This can be tricky enough with a regular group, and is nothing sort of an exercise in frustration if you play in weekly pick-up games at your friendly local game shop.
(4e has a similar system, with the concept of things like Tribal and Guild feats, where you spend feat slots to gain abilities that increase in power if other party members also have the same feat. Unfortunately, most of them aren't very exciting, which leads me to believe they were originally designed as a DM option that could be added on to an existing group like Teamwork Benefits before it got shunted over into the feat section- otherwise most of them just really aren't worth it if your DM isn't going to be handing them out as an accent to highlight your particular group's way of doing things.)
So, what happens if you take a Teamwork feat and no one else in the party does? Well, most of the time, you're up the proverbial creek without a paddle. Still, in their attempt to get people using the system, they did include some options. The Cavalier class designed to favor mounted combat and challenging foes, also has the Tactician ability, granting Cavaliers a Teamwork feat as a bonus feat and letting them share it with allies within 30 ft for a few rounds per day based on level, and do this a number of times per day equal to one plus one per every five levels gained. As they level, they gain additional bonus feats and can eventually share up to two of any of their Teamwork feats as a swift action instead of a standard action when using this ability. Of course, this only means you can benefit from your Teamwork feats for a very small amount of time each day at the earliest levels, which isn't much help if you get into multiple fights.
This is not an uncommon ability. The helpfully-named Tactician is a fighter archetype that improves the fighter's skills somewhat, adds a few minor bonuses that require way too many levels in order to pay off, and lets the fighter pick up additional Teamwork or Skill Focus feats with fighter bonus feats. Unfortunately for the tactician, investing heavily in Teamwork feats is all but doomed to failure in most parties, since very few characters can afford to keep up with a fighter when it comes to feat expenditure, so investing in a pile of Teamwork feats won't accomplish all that much. True, it gives you more options for your Tactician ability, but if you've got a pile of teamwork feats you've probably spent well past the point of diminishing returns for an ability you use four times per day. In fact, it's doubly troubling since the Tactician only gets the Tactician ability, and not the Cavalier's Greater Tactician or Master Tactician abilities, so it's not hard to argue that the only feat you can share is that single bonus Teamwork feat you got with Tactician. It's a hard life for a fighter.
If you want to see one of the pinnacles of Teamwork, look no further than the Inquisitor another class introduced in the Advanced Player's Guide along with Teamwork Feats (and the Cavalier). The Inquisitor receives a bonus Teamwork feat every three levels, and can choose to spend a standard action a few times each day to replace the Inquisitor's most recently-gained teamwork feat with a different one, effectively granting the Inquisitor a "try before you buy" set-up when it comes to teamwork feats. The Inquisitor also gains one special ability- Solo Tactics. This ability lets the inquisitor treat all allies as though they had the same Teamwork feats as the Inquisitor for the purpose of activating the Inquisitor's own feats. Since "allies" is a fairly wide category that can include everything from fellow party members to animal companions to familiars to summoned monsters, this ability offers quite a bit of flexibility. So the class that gets the most out of Teamwork feats is the one that doesn't really need to act as part of a team and doesn't need to devote much in the way of effort to learning teamwork.
Similarly, valet familiars are considered to have the same Teamwork feats as their owner, which can be fairly handy if you've got the right Teamwork feat and familiar (your average familiar won't help all that much with combat feats, but the right familiar can).
Out of all the teamwork users, perhaps the only class that can even make an effort to really work as a team is the paladin. Specifically, the Holy Tactician archetype, who doesn't get as many bonus teamwork feats as some of the others, but does have the ability to hand out a teamwork feat the paladin possesses as a bonus to allies within 30 ft. While I suspect it's supposed to be a "you have this bonus feat as long as you're within 30 ft or until the paladin changes it" but there's not really a listed duration or distance other than the requirement that you be able to see and hear the paladin. So you could stand next to a paladin during the war, go off and live your life, then catch sight of the paladin in a crowd and then it all comes back to you.
So, assuming you and your party can somehow settle on some Teamwork feats, what exactly can you get?
Well, it varies.
Some of them are oddly specific. Brutal Grappler, a feat that allows you and your allies to all damage a creature that you're all grappling instead of limiting it to just one of you. Grappling is already a rather specialized fighting style, and this one not only requires you to have multiple people who share your hobby, but that all of you also be orcs or half-orcs, making it a rather DM encounter-specific gimmick feat unless you can somehow convince your friends that the world is facing a dire shortage of orcish luchadores.
Then you have a feat like Combat Medic. Character focused on providing medical aid in the heat of battle- sounds like a solid-enough concept, right? As for the feats effects, when you use the Heal skill to provide First Aid to stabilize a character who's bleeding to death or treat caltrop injuries or poison, you can take 10 to achieve average results and don't provoke Attacks of Opportunity when doing so. Attacks of Opportunity represent you basically blundering into the path of an enemy weapon or providing a large enough opening due to being distracted that the enemy can take a swing at you, but how often do you make Heal checks to stabilize or remove caltrops while under fire compared to just having someone cast a healing spell for far greater effect? While taking 10 is good for getting an average, dependable result on a die roll, treating caltrops and stabilizing characters is DC 15, something that most healers can effortlessly hit by mid-level. Poison does tend to scale up in difficulty as you level, so taking 10 and avoiding AoOs at higher levels could be somewhat useful, but then again immunity to poison isn't too hard to pick up via spell or magic item. Still, not everyone reaches high levels, so maybe a low-level character would get some use out of it as a day-to-day non-magical healer who tends to the wounded. One tiny little problem though- Combat Medic is still a Teamwork Feat, and thus requires the subject to also have the feat... so Combat Medics can only treat other Combat Medics. "Physician, heal thyself" indeed. Unless you've got a Holy Tactician or Solo Tactics, good luck getting any use of this one.
Enfilading Fire is a feat that allows you to get a +2 bonus to your ranged attacks when one or more allies are flanking a foe. A fair enough concept, and several feats like this exist in games such as 4e to allow ranged characters to benefit from their allies' tactical positioning. Unfortunately, this is still a Teamwork feat, and thus you're only going to get a bonus from other people who also have this feat. This wouldn't be a problem, except this ranged feat requires you to go two feats into being a ranged attacker plus have another teamwork feat before you qualify. So if you want someone to rustle up a hit bonus for you, you're going to have to convince them to spend four feats, at least three of which aren't going to be all that useful if they're going into melee to flank enemies. There are very few characters who can justify this expense (four out of your ten feats for characters who don't get bonus feats) just so you can have a lousy +2 to hit. It's nigh-unusuable without Solo Tactics or some way of sharing your teamwork feats such as Tactician (Holy or otherwise).
Moving on from the valley of broken toys we get into the plains of nominal usefulness with feats that let you do things like emphasize cavalry maneuvers or bolster your defense against combat maneuvers, or even get an impromptu musical ensemble going on if you decide to play as Josie and the Pussycats. But lets get to the more thread-worthy feats.
Stealth Synergy a feat that lets you make a stealth check using the highest d20 roll between you and any other ally with this feat that you can see. In theory, this can lead to some nice numbers, since it effectively lets you roll Nd20 taking the highest for your stealth checks, enabling a ninja team to be very hard to detect. Of course, as some of you might have already noticed, there's a weird disconnect connect when you've got a stealth-based feat that relies on your ability to see other stealthy people. While this is totally doable if you and your buddies are sneaking past guards while crouching behind a low wall (where line of sight is blocked between you and the guards, but not you and your friends), it's more confusing if you're sneaking around in the fog or something- if one of your friends rolls a natural 20, the stealth check may be so good that the rest of your allies can't see your stealthy friend any more, and thus can't benefit from your teamwork. Presumably your allies will call you out for being a loose cannon, but a damn good ninja.
While we're on the subject of stealthiness inhibiting teamwork, the pixie is a small fairy with permanent invisibility, but no way to see invisible creatures- how do they interact with one another? True, they can suppress their invisibility, but how do you know when to let your invisibility down? Do they have some sort of third-party site to arrange meet-ups? Do they worry about someone pretending to be someone they're not in communications, or that at any given moment when they let their glamor down in their most private of times, there may be an invisible pixie silently hiding somewhere in the room? Watching them. Judging them.
And now, another momentary educational diversion. Today's subject: Action Economy. Action Economy refers to the interplay of turns and both what and how much you can do on a given turn. The action part refers to the different kinds of actions you can take during your turn, like attacking, defending, casting spells, moving, using items, running away, etc. The economy comes from the fact that you are normally only limited to a certain number of actions per turn- you normally can't cast every spell, attack all your enemies, use all your items or travel an unlimited distance in one round. The opposition is normally similarly limited, and in any given encounter, you and your opponents spend actions in order to reach your objectives, possibly using your actions to halt your opponents if their objectives run counter to yours. When it comes to things like fights, a fight doesn't really end when you knock out all of your foes; rather, it ends because you've rendered all your foes unable to do anything to stop you, and death or unconsciousness is merely a rather long-term way of ensuring that- if you killed a foe only for it to announce "behold my true power!" and turn into a spooky ghost wizard then you've now got more problems on your hands.
Solid understanding of the Action Economy is a great way to improve your group's efficiency in combat, enabling you to take on greater challenges and expend fewer resources. When it comes to the action economy, there are many ways to limit the actions your opponents can take, the most obvious being murdering the hell out of them. Due to the way the HP system works, an opponent at 100% HP in Pathfinder fights as well as an opponent at 1% HP, but an opponent at 0% HP or lower is usually out of the fight. Thus, all other things being equal, it's usually beneficial to focus your damage on one target at a time instead of spreading it around. So if you have a party of four against four opponents, the default strategy is usually to dogpile one opponent to take it out of the fight, while if you can make multiple attacks and are facing multiple foes, it's usually better to pile it onto one foe to take it out of the equation, since three injured foes have as many actions as (and thus are usually as dangerous as) three healthy foes, but two perfectly healthy foes and one dead foe are less of a threat to your team.
But when it comes to action denial, there are many possible ways to limit your foes' possible actions through control abilities, chief among them being status effects. Dead is usually the most effective status, but having a foe knocked unconscious or stunned or dazed is a form of crowd-control that can hard-lock an opponent out of a fight for several rounds, which can be pretty effective if you've got party members who can take advantage of the temporary inconvenience to upgrade your foes to a more permanent state of inaction. And while hard control effects that flat-out prohibit all action are incredibly useful, soft-control effects that merely prohibit a foe's most effective action action can be just as helpful. A big club-swinging ogre may hit like a truck, but that's all for nothing if it's out of melee range and can't move due to having its feet stuck to the floor. Or if there's a wall of fire between it and the party. Or if it's fallen and can't get up. Or if everyone is flying.
Opponents miss 100% of the attacks they never make, but past that, there's the more risky method of reducing the odds of success for actions your foes actually take. Leaving a foe weakened or penalizing its attack reduce the odds of a successful attack, though even the most inaccurate attack has a 5% chance of success thanks to the "always hits" property of a natural 20 on your attack roll's twenty-sided die. But even that can be thwarted through concealment, which can give a 20% to 50% chance of missing, so there's always a chance of even more disappointment if you roll for concealment at the same time as or after you roll for an attack. The odds can also be tilted in your favor by bolstering your own defenses- in most cases a bonus to your AC is about equivalent to a penalty to your opponent's attacks (though accuracy penalties are usually safer because there are a variety of possible attacks and maneuvers that can target different defenses).
Not only can you penalize the actions of your foes, but you can bolster your own actions. A big enough boost to damage means it will take fewer attacks to drop an opponent, while a boost to accuracy reduces the chances of you choking at an inopportune moment. A spell such as haste is interesting because not only does it boost your attack accuracy and defenses, but also your speed so that you can close into range faster or maneuver around obstacles better, and also gives you an extra attack per round to ensure that it takes fewer turns to drop your foe. Interestingly enough, haste in 3e didn't give you an extra attack when attacking, but an extra standard action. This meant that a fighting character could move full speed then full-attack, or maybe attack and attack again or attack and activate an item... but it also meant that a caster could cast two spells per turn. Items that gave out permanent haste were nice on a fighter, but ludicrously good on a caster who could pack more power into every action. That's the power of extra actions- they're basically extra turns. The more extra actions you can scrounge up, the faster you can stop your enemies by either using abilities to take away their actions or simply pounding them into the dirt.
Spellcasters are often the best at this, since they can whistle up summoned allies so you can have more actions to attack with each round, while spells such as dominate person represent a serious action advantage because they not only stop the opponent from taking actions against you, but turn those actions against your other opponents. Back in 3e, the Tome of Battle: The Book of Nine Swords supplement introduced the system of martial maneuvers, basically special attacks and abilities for a certain type of combat character that ranged from extraordinary variations and upscaling of things they could normally do to abilities that were basically supernatural in essence. Anyways, among those abilities was the infamous (and confusing) Iron Heart Surge. Perhaps less infamous but no less noteworthy was the ability known as White Raven Tactics.
The Book of Nine Swords posted:
White Raven Tactics
[...]When you use this maneuver, select an ally within range. Her initiative count immediately equals your initiative count-1. She then acts on her new initiative count as normal. If she has already acted in the current round, she can act again. If this maneuver would not change your ally's initiative count, it has no effect. If she has not yet acted during this round, her initiative count changes, and she acts on that count as normal. She does not act again on her original initiative count.
What a magical phrase. Characters with this ability could wait until their allies went, then use it to give their allies a second turn, letting them stack turns before enemies had a chance to react. Fighters could pound away at foes, while casters could end the world. There are some even goofier options that involve exploiting some other sub-rules, but those are for another time. The important point to take from this is that extra actions are incredibly good at tilting the odds in your favor and are generally worth their weight in gold on a character who can take advantage of them.
So why am I talking about all this in a write-up about Teamwork feats? So you'll understand what's yet to come.
There are six Teamwork feats that can be basically called "the good ones" owing to the fact that they don't just give you extra pluses to hit or whatever, but they actually give you extra attacks. Before I continue, honorable mention goes to Lookout, a feat that lets you act in a surprise round as long as you're adjacent to an ally who wasn't surprised, though if both of you could act normally without the feat then it lets you take a regular turn during a surprise round instead of a partial turn. Normally it's in your best interest to use appropriate scouting to avoid being surprised by your enemies, but if you're stealthy enough you can gain an turn advantage over enemies when you launch a surprise attack, since you can fully unload while your opponents are limited to a single action. While a rare enough occurrence not to be worth spending a use of Tactician on, it's still solid enough that a Holy Tactician might find use for it as part of the Battlefield Acumen ability to ensure the party has a better chance in surprise rounds before switching it over to a different ability once regular combat ensues. Thus one of the best characters for launching an ambush is a paladin. Now, onto "the good ones."
The simplest of these would be Target of Opportunity, lets you make an additional ranged attack as an immediate action whenever an ally with the same feat makes a ranged attack against an opponent within 30 ft of you, basically letting you shoot someone even when it's not your turn (though you only have on immediate action each round). So if you have two people with this feat who are attacking fairly close opponents, that's two extra attacks each round- not bad, especially if you can get more friends in the shooting business (though owing to the restrictions on making the attack, you're going to want archers instead of axe throwers). The prerequisites are incredibly basic and easily hit by anyone who's considering a career in archery, but if you've got Solo Tactics or some form of Tactician then you can start handing it out to people who aren't even archers, and trigger it off of the ranged attacks rolled by casters when they cast things like rays that drain or disintegrate their targets, since ranged touch attacks are still ranged attacks. Fun times.
Coordinated Charge is a similar feat, one that allows you to make a charge attack as an immediate action whenever an ally with this feat charges an enemy who's within your short charge distance. Charging is nice because it lets you move a fair amount and still make an attack, or at least that was the original intention. Thing is, developers quickly introduced elements that bolstered the power of a charge attack from being a single conventional hit. One such element would be the Spirited Charge feat, which let you deal triple damage if you made a charge attack while mounted and wielding a lance, making your big hits even better. Another ability of note is Pounce, which lets you make a charge attack and make multiple attacks on the charge instead of just one. Normally reserved for large predators such as tigers and the like, it's fairly painful when a big cat slashes you five times with its claws and fangs, but it's even more painful when in the hands of a barbarian, whose big honking magic sword is probably going to hit far, far harder. Funnily enough, these two abilities stack, allowing a mounted barbarian with a lance and Spirited Charge to make several triple-damage hits on a charge, a strategy cunningly named RAGELANCEPOUNCE.
In 3e, charge optimization could get even bigger, as you could pick up spells and items that doubled your damage on a charge, stacking with Spirited Charge to turn it into a 4x or even 5x damage hit (due to the way stacking multipliers worked in 3e), combined with feats that gave you a massive bonus to damage on a charge, while taking a level of barbarian to pick up the ability to pounce and multiply your damage further. It was not uncommon to be able to do thousands of points of damage to a target from one round of charging as you hit your target like a freight train. But even if you aren't devoted to charge optimization in Pathfinder, Coordinated Charge still lets you get your close-quarters combatants into the fray and dealing damage, freeing up their normal turns so that they can attack normally instead of wasting a round closing in. The feat's prerequisite of having two other Teamwork Feats before you can take this one is a harsh one, but it's still an absolutely prime choice for sharing through a Tactician (Holy or otherwise).
Past that and we get into a new realm. Seize the Moment is a feat that lets you make an Attack of Opportunity whenever an ally with this feat scores a critical hit on an opponent within reach, and since it has Improved Critical as a prerequisite, that's a going to be a fair number of attacks, while Outflank improves your flanking bonus when you flank with a partner who has this feat, and also lets you make an Attack of Opportunity against a target if your flanking buddy scores a critical hit on it. Attacks of Opportunity are basically free attacks, representing your ability to seize the moment or what happens when an opponent stumbles into your whirling weapon after letting its guard down. More attacks are never a bad thing, though between the two Seize the Moment is probably the better bet if you can get allies who meet the prerequisite, since it doesn't require as much of a precision formation as Outflank (which can be hindered when you run into enemies who can't be flanked).
Broken Wing Gambit represents an unusual option. Whenever you hit someone with a melee attack and have this feat, you can elect to give that target a +2 to hit and damage with the next melee attack it makes against you in return, but that attack causes the target to provoke an Attack of Opportunity from each ally with this feat who's within reach. Now, an ability that modifies the target's hit chance and provokes a retaliation strike against the target if the target goes for the wrong ally might sound sort of familiar to some of you, since it's not entirely dissimilar to parts of the defender systems in 4e.
Now, D&D and its kin have had a long-standing tradition of stashing the squishiest members of the team behind the party tank, but there was very little actually keeping your opponents engaged with the meat shield other than the layout of the battlefield and maybe a gentlemen's agreement with the DM. Well, not entirely- melee combatants did have some degree of danger to keep others in the fight, since characters could make a free attack against anyone who fled the melee, or all of their attacks if they had more than one. Characters could choose to withdraw from a fight and move up to 1/3 their speed without any further penalty, although their opponents could follow at 1/3 their speed without any penalty either. This was combined with some other rules regarding things like ranged weapons and spell failure to form 3e's Attack of Opportunity system.
The theory behind the Attack of Opportunity system is that a free attack on your opponent should be enough to discourage your foe from bypassing your frontlines and diving into the back. The reality behind the Attack of Opportunity system is that unless you're seriously built for it, a free swing from your fighter is a fair price to pay for a chance to disrupt the caster- a fighter's sword can only take away your hit points, but a wizard's spell can take away your turn. Unless the fighter can kill you with a single attack, it's usually safer to bypass the fighter, and even if the fighter could one-shot foes there was an upper limit to the number of attacks of opportunity a fighter could make in a round, so a sufficiently large swarm of kobolds or goblins could blitz past the fighter without further problems if they didn't mind stepping over the corpses of their fallen brethren in the process.
Now, 4e attempted to give the front line more teeth in the form of a system wherein certain characters and classes could mark their targets, providing the target with a -2 penalty on attacks that didn't include the marking character, representing the idea that the threat of the marking character consumed the target's attention. That in and of itself isn't entirely enough to make the grade, so if the marked target still attacks someone other than the marking character, the marking character usually has some sort of retaliation attack or punishment ability to take advantage of the lapse in focus (not unlike AoOs). This presented opponents with a tough choice- either go for the squishies and risk lower accuracy and punishment or dance with the defender and try to figure out a way past the defender's tough defenses and high HP count. Marking was inspired by the strategy of the same name used in basketball and football, though for some mysterious reason sporting analogies were completely lost on most of the RPG fanbase. Who knew?
Of course, Broken Wing Gambit is still rather different from 4e's defenders in several important ways. One of them is that you have to have the Teamwork Feat and you have to fight in melee against a target in order to set this up and make it unattractive to hit you, so a Pathfinder Wizard is unlikely to get much out of this compared to what a 4e fighter can do for a 4e Wizard. The other important factor is that in 4e marks are not supposed to stack in order to prevent the target from being forced into a Catch-22 situation where the target gets stomped by two or more defenders. As it turns out, this doesn't actually work, as many defenders have non-mark-related options to inflict some pain on their foes and you can seriously pinball an opponent around with them- paladins in particular are pros at punishment-stacking and can hand out the most righteous ass-whupping of your rapidly-shortening life if you ignore them. But while 4e defenders stack by accident, Broken Wing Gambit stacks by design- if you have N characters with this feat who activate it on a target, that target will provoke N-1 attacks of opportunity on its next attack if it strikes a Broken Wing Gambit character. The more you stack it up, the funnier this gets, though everyone has to at least hit with one melee attack in order to set up a proper catch-22 scenario.
Now, those of you who have been keeping track, I mentioned that there were six good attack-enabling Teamwork feats and have only mentioned five. Well, number six is Paired Opportunist. When adjacent to an ally with this feat you gain a +4 bonus to attacks of opportunity, and more importantly you can make an attack of opportunity against any against any creature within your melee range that provokes an attack of opportunity from your adjacent ally. Now, on the surface this isn't actually all that interesting, as normally your opponents dictate when you can make attacks of opportunity by choosing to do specific actions such as moving, spellcasting, or making ranged attacks (though characters sufficiently invested in any of those things will usually have abilities that prevent them from provoking while doing it) and if an opponent within your reach provokes an attack of opportunity from an adjacent ally through moving or whatever, it probably also provokes an attack of opportunity from you.
In the context of actions that normally provoke AoOs, this feat is not that great since it basically provides a +4 to hit on those attacks- nice, but not really worth building a team around since you can't control how frequently you'll be able to make AoOs. However, this is Pathfinder, and if there's one thing Pathfinder likes, it's jury-rigging existing systems to create new functions, and "provokes an attack of opportunity" is a piece of language that shows up in some unusual places... such as the AoO Teamwork Feats I mentioned earlier.
While Paired Opportunist doesn't do much for conventional AoOs, what it does do is give you access to AoOs you otherwise have no goddamn business messing with. Consider a party with Paired Opportunist and Broken Wing Gambit. Normally, if N party members are engage in melee with an opponent and activate the feat, then the opponent provokes N-1 AoOs when it makes an attack against a party member, but if the party members have Paired Opportunist and are all adjacent to at least one other party member (such as by forming a line that snakes around the target), then when the opponent provokes an AoO from the other party members by attacking someone, it will also provoke an AoO from the target it's attacking. While this turns it from N-1 AoOs to N AoOs, more importantly it's a melee attack, which means that the target can use the opportunity to reset Broken Wing Gambit against the opponent's next attack, which means as long as you can keep hitting, every attack the target makes will provoke N AoOs from your team (for comparison, Broken Wing Gambit is normally N-1 AoOs, but after they're made the opponent can keep swinging at the target without fear of further retaliation). Considering many monsters are balanced around the idea of making more melee attacks than humanoids but with their individual hits being not as damaging as weapon attacks, this exchange of blows severely favors the party (especially since AoOs interrupt the triggering action, so your counter blows can land before the enemy lands an attack).
Outflank offers a similar opportunity. If you have characters who are adjacent to the target and are somehow flanking it (either through a formation that links the two flanking characters through a chain of bodies, or with the use of a feat like Gang Up), then a critical hit scored by one of the flanking characters will cascade through the chain, getting back to the original character who can make an AoO as well, and if any of these AoOs score a critical hit from a flank, the whole chain starts again.
It would be even easier to do this with Seize the Moment, but that brings us into an exciting episode of "Rules Lawyer Theater". Paired Opportunist states that enemies that provoke an attack of opportunity from your allies also provoke an attack of opportunity from you, but Seize the Moment merely states that when an ally scores a critical hit against the target, you may make an Attack of Opportunity, not that it provokes an Attack of Opportunity from you. This means that under a strictly literal reading of the ability it doesn't work, and also rules out some fun class features like the rogue's Opportunist ability, which lets you make an AoO against a target who's been hit in melee by one of your allies- if it said that it provokes an AoO then it would allow one attack from the rogue's allies to trigger an AoO from everyone in the chain including the original attacker.
While this bit of exact language may rule out a few fun options, it's certainly not the end of the world. Cavaliers of the Order of the Star have a high-level ability that provokes AoOs against anyone who makes an attack against the cavalier or adjacent ally of the same faith, while Barbarians can take Come and Get Me as a rage power that makes enemy attacks provoke AoOs and allows them to basically cross-counter their foes before the foe can finish an attack ("kill it before it kills you" is a great defensive ability, even better than armor). When combined with Paired Opportunist you can get a lot more bang for your defense, and who knows how this stacks with Broken Wing Gambit (Paired Opportunist does not let you take more than one AoO for a given action, but is the given action "an enemy attacks, provoking an AoO" or is the action "ally activates Come and Get Me" and then "ally activates Broken Wing Gambit" as a new action?)?
Combat Maneuvers are also a prime source of AoO generation, as many of the "Greater" feats for any particular manuever (Trip, Overrun, Reposition, Drag) also cause the enemy to provoke AoOs from one or more characters, which can be chained through Paired Opportunist. Viscious Stomp is another feat that makes enemies provoke AoOs from you if they fall prone in an adjacent space (including through things like slipping on a grease spell), and can stack with feats like Greater Trip or Greater Overrun to allow your party to start a hoe-down on a fallen enemy's face for something like 2N AoOs in response to a fall (while your Vicious Stomp AoO must be unarmed, their Paired Opportunist AoO is under no such restriction).
Now, a party that builds around Paired Opportunist is going to run into a problem- you only get one AoO per round. Combat Reflexes adds your Dexterity modifier to the number of AoOs you can make per round, but even the most Dexterity-focused character is only going to get another 10 to 15 attacks out of it, with Strength-focused characters probably hovering somewhere around three to five extra attacks. But things get a little more interesting if you're playing the Mythic Adventures subset of the Pathfinder rules, which is supposed to make your adventures more epic and heroic like heroes of mythology. While I'll go more into details in a later post, one of the possible feats you can take in the game is Combat Reflexes (Mythic), which completely removes the cap on the number of Attacks of Opportunity you can make in a round. Another is the ability Press the Advantage, which is like Seize the Moment in that it generates AoOs from allied crits, except that it uses the magical "provokes" phrasing, allowing it to be chained through Paired Opportunist. Put them together in a party armed with weapons that have the highest crit range (kukri, cutlass, rapier, scimitar, falchion, fauchard, wakizashi, katana, nodachi) and each attack has about a 30% chance of being a critical hit and cascading into another round of attacks. The more people you have making attacks, the greater the chance you have of making more attacks.
On its own Paired Opportunist has little merit, but if your party is willing to go whole-hog into finding ways to make enemies count as provoking AoOs then it's a force of destruction. In fact, one of the problems you might have is that you're just killing people too damn quickly, and Paired Opportunist isn't of much use unless you're adjacent to an ally and you both have the same enemy in reach, which can be a problem if you're standing side-by-side and your reach doesn't entirely overlap. This isn't likely to be a problem in a fight against a big beefy solo opponent like an elder dragon or the Tarrasque, but a cascade of AoOs is overkill against more conventional foes. Now, you could use something like Combat Patrol to boost your reach and shift around so you can strike at different enemies as the battle progresses, but there's one other possible route. Reach is not just a question of the area of a horizontal plane, but also a question of volume- creatures can apply their reach above and below their space. In particular, Small and Medium creatures both occupy 5 ft squares with 5 ft reach, so there's nothing stopping a halfling ninja from riding around on a half-orc barbarian to make sure that they will both be able to make AoOs against everything within reach of the other and combine it with Broken Wing Gambit or Come and Get Me to ensure that any retaliation will be harshly punished.
That's Teamwork for you: On one end of the spectrum you've got the most malfunctioning medical team in the realm, on the other you get the Master Blaster Razor Disco that lets you kill the Tarrasque in one round on someone else's turn.