A new transformation technique

[Madara Uchiha]

i was wondering i wanted to do this for a DBZ mod i am working on i want to do something were if a character transform it takes down his mp then if it reaches zero he transforms back i have thought about somethings like were the transformed character has a certain bdy which can only be hit when mp goes to zero but that doesn't work because i put it in the standing frames you see but then they just transform back when they transform so can someone help?