Let me tell you of the two person synergy build that me and a friend came up with that is the most broken thing ever. Since you can stack up truly stupid multiples the raw damage comes out to to be several thousand at lvl 20.

One person is the best crit fish that you can make doesn't really matter how just pump there chance to score a crit as high as you can go and give them butterfly sting so they can pass that crit over to someone else.

2nd person is a Gendarme a cavalier archetype. Pick up things like power attack, spirited charge and any other feat that deals with lances or increases crit damage either top or multiple.

At lvl 20 the first person sets up a crit and passes it to the cavalier. The cavalier charges when we did the calculations with a normal lance the damage capped out at something around 4,000-5,000 it one shot every single monster in the book several times over. Complete overkill. Fyi at lvl 20 every crit a Gendarme makes with a lance is max damage so what ever it hit is guaranteed to be dead. Just be careful of spells that redirect damage like hostile juxtaposition or you will end up turning your allies into red mist instead of your foes.

If you can convince the 3rd guy to be a gunslinger that uses shotguns and have them do a stun lock build. I forget how to do it but one of my friends made one. It also relies on crits if I remember right but instead of dealing thousands of damage it instead gives out status effects that effectively skip the enemies turn and make them easier to hit.

The most broken builds in existence rely on multiple people working together to pull it all off.