This idea came up while reading ClashBlades topic about Overdrive and Limit Break actions for the each party member just like in older FF games.

The idea about party attack is instead of a (can coexist too i think) individual overdrive attack, having a one big party attack.

Basic requirement for it to have a Light or Full party.

So what is it?
It is basically an uber charged move casted by whole party. It can be something cinematic where all pt members circle the enemy and do a WS or some kind of animation to unleash a summon.

So how it works;

1. Party engages in fight. Kills the mobs. With each dead mob points added to OD bar and it starts to fill.
2. Party disengages or just in passive mode. OD points start to decrease.
3. Party starts to fight again with a new enemy or rushes to a new enemy to avoid OD points to reach zero. And after the kill more point added.
4. OD bar is full and party is ready to unleash it. It can be activated like in Battle Regiments. Everyone does it and bam..super move is initiated!

So this super move can be something like a HP boost, or filling hp of every member for like 20%, it can be some defense buff, it can be a SUMMON! So the cinematic part can be triggered there. When party casts the attack. Screen fades out and in back and it shows every pt member circled around the mobs and doing some animation. Ifrit shows up from sky slams the mobs and leaves. And everything back to normal.

To keep the things more interesting there can be different variations of these. Like offensive ones and defensive ones. One problem with it is people may spend too much time about discussing which one to use every time they form a party. So it must be more streamlined, simple to execute and NOT game breaking with its effect.

And its effect on gameplay and mechanics would be making people to form parties more often, more dynamic battles and rushing for enemies in the maps, saving up OD points for major battles can be a nice strategy.

Also it can be super complicated by mix matching each class weapon skill in to it, more timing based, as i said before more types for more strategies.

But i like the idea of summons more than buffs. at least it would be fun to watch (and must be really short).