I always considered Anima's Overdrive "Oblivion" in FFX to be my favourite attack. First of all the character design is badass, and secondly the attack destroys entire parties with ease. What a shitty way to go though - getting punched repeatedly by some angry hairball that is fused to the bottom of a very angry fish-mummy-wrap-chained thingy.
Couldn't find a gif for it so here is a picture of Anima; I'll try to find a gif later
*edit* Here are all of the aeon overdirves in ffx; all very badass, but Anima [2:14] is the best
https://www.youtube.com/watch?v=o-TAnVgsWnY