Quote Originally Posted by Skyblade View Post
Wasn't that because it takes 1000 MP for four castings, and the max is 999? I thought you could Quadra Magic it with MP<->HP.
Quadra Magic doesn't require any more MP than a normal cast, so a MP limit isn't the reason. You can use it on all magics and summons with the exception of KotR (too overpowered, like sora_lion_heart said) and Escape (pointless).

It halves the damage of the attached spell, but if you equip five instances of Quadra Magic and an identical magic or summon materia you can get eight castings in one turn. I don't know if it's possible to get sixteen in a single turn with W-Magic/Summon so if anyone wants to test that I'd be interested in hearing the result.