I love teamwork on the table, but it's one of those things that the Pathfinder rules don't promote as much as I'd like.
A few years ago,
BadAxe Games put out a supplement called Trailblazer. I recently discovered it while wandering down an internet hole that started at a post on the
Pathfinder Google+ community. The folks at Bad Axe apparently had the same thought as I did because they created a great set of rules called Combat Reactions.
A combat reaction allows you to take certain actions even when it isn't your turn; attacks of opportunity are a classic example of a combat reaction. Trailblazer pulls actions like Aid Another into the same family as AoO, allowing characters to use their often-wasted AoO to promote teamwork on the field.
Around the same time I discovered Trailblazer, I read an intriguing post from gamer and blogger
Brandes Stoddard at
Harbinger of Doom on what he calls 'Giving Ground,' a technique that fits beautifully under the combat reaction umbrella.
I've adopted both of these ideas, tweaked them a bit and will be playtesting them in my Jade Regent game soon.
Combat Reactions
Combat reactions allow you to perform special actions any time during a round, not only on your own turn. Combat reactions are considered immediate actions and you may take 1 combat reaction per round at 1st level. You gain an additional combat reaction when your Base Attack Bonus (BAB) reaches +6, +11, and +16. The Combat Reflexes feat gives you a starting number of combat reactions equal to your Dexterity score.
Aid Ally
If you are threatening an opponent that is engaging an ally in melee combat, you can assist your ally as a combat reaction. Multiple allies can aid the same target.
Aid ally combat reaction bonuses stack with each other, but not with other circumstance bonuses.