yes Penance has an overdrive guage of sorts like Nemesis one in that its invisiable he will only use it in the second stage of the battle when Both his arms are alive.

the move is called JUDGEMENT DAY and is arguably the coolest move ever seen in a Final Fantasy game. i,ve never seen such gorgeous graphical effects as when the move hits. it wipes out 99,999 hp and 999 mp. i also think it wipes out auto life like Dark Yojimbos Zanmato and Dark Magus Sisters Delta Attack but even if it did,nt the arms would finish you off. it impossible to beat Penance without killing his arms anyway so you can stop him using this.

so yeah the greater dark Aeons (Bahamat, Anima, Yojimbo, Magus Sisters) really are a million miles ahead of Nemesis. but Penance in turn are so far ahead of even the Dark Magus Sisters its scary.