Supernova: Limit or Summon? Potential Spoilers
What do you think? Limit Break or Summon?
I say it's a limit break... Why exactly would Sephiroth carry around materia at that stage anyway? Besides... it seems Sephiroth has only enough MP to cast Wall on himself. Give him an ether in the middle of battle, and he casts wall again.
Other than that, in Nibelheim, during the flashback, he has materia, but he doesn't actually use his mp...
Another thing, yeah, he does Supernova regardless of how many times you attack him... but he could be set on a time schedule, meaning he'll use it after a certain number of rounds.