"Turn" Triggers in Battle

[Blazer-X]

Not really sure if "turns" is the right term, but basically, I want to create some kind of condition or script that is triggered whenever you gain control of your character. More specifically, I want to create a "state/status" that "drains" your character's MP/Magic-Points each turn, until your MP/Magic-Points reaches zero, which is when the "state/status" is removed.

If a tutorial for such a trigger has already been posted in another thread, please link me to that thread.

Thank you in advance.