[Trigger] How could i do this?

[Twisting]

So in this new map im making i have the metamorphasis spell to turn a unit into another unit for a period of time BUT i wanted to add a twist to the spell that when its cast a nearby alled hero would "dissapear" for the time the spell is on the caster but i dont know what actions i should do to make this work or how to make the game choose an ally and not an enemy. i tryed a few diffrent ways to make it work but they all ended up deleteing the unit involved or something...... so could anyone show me a good way to make this work?

 

[graystuff111]

the action is Unit - Hide Unit