I was in a 60 Grift and one of the party members would gather up trash mobs and then do this finishing move that seemed to kill everything in one shot (think it was the monk). What is the build/move? That seems like fun.

Exploding Palm/Seven Sided Strike

This one?

http://www.diablofans.com/builds/57405-quin69-gr71-ulianas-monk

I think it's sunwuko ep monk that blows the whole screen up at once.

Uliana monk is also a possibility.

It was likely a sunwuko EP monk

Ulianas 6 doesn't have the same pop as an EP monk does. If it was wiping out entire groups at 60+ it was prob sunwuko because of the way that build stacks exploding palm dmg.