Mind control magic.

[Teldrin]

I'm making a banshee boss with the ability to control other units, I have to make a trigger for that, and there's one more detail that the fact that this ability is a possession means the banshee enters the unit's body and controls it, I don't know how to make that work and above all, it will not be eternal, as it should last about 10 seconds at most.

 

[Chaosium]

I'd do something like this

• Possess
  • Events
    • Unit - A unit Starts the effect of an ability
  • Conditions
    • (Ability being cast) Equal to Possession // any dummy single target spell would do
  • Actions
    • Unit - Hide (Triggering unit)
    • Unit - Pause (Triggering unit)
    • Set VariableSet Target = (Target unit of ability being cast)
    • Set VariableSet OriginalPlayer = (Owner of (Target)
    • Unit - Change ownership of Target to (Owner of (Triggering unit)) and Change color
    • Wait 10.00 seconds
    • Unit - Change ownership of Target to OriginalPlayer and Change color
    • Unit - Unhide (Triggering unit)
    • Unit - Unpause (Triggering unit)

This is assuming only 1 instance of the ability can happen at once. You use variables to keep track of the victim and the owner, make the boss invisible and not do anything while it's active, then restore everything back after X seconds