This seems a bit simple and might work for you but did you try combining trigger once and destroying the projectile if it hits even one enemy?
Hey Destitute, thanks for the response.
I should have mentioned that the "Fireball" object is supposed to be like an explosion, that stays on the screen for a few seconds, and damages any enemies that touch it.
I think I've found a solution.
What I've done is every time a "Fireball" is created, I create an Array with an "ID" variable that is set to that Fireball's UID.
Then if an enemy touches it, it deals damage then adds the enemy's UID to it's array and won't damage it again if that UID is on it's array.
Then when the fireball is destroyed, so is it's array.
So far it seems to be working and I haven't found anything wrong with it.