I think you'll need to provide a bit more detail. I'll give a suggestion, but if you want something else you'll need to explain.
Suggestion (active iff MP < 1): make a state with the appropriate traits and grab Yanfly's
Auto Passive States plugin. This plugin provides a notetag for states to let you set when the state's effects are active. Add this line to your "zero MP debuff" state's notebox:
Code:
<Passive Condition: MP Below 1>
Then simply add this state to the Actor Passives List in the plugin parameters so all actors have it.
