Here's another problem with instances...
I tried to make some enemy ai:
The enemy keeps going left until he comes close enough to the player; then, after a little delay, he either swings his club or he goes to the right for a short interval and then swings his club, after that it's back to going to the left looking for the player again.
It works fine with one enemy on screen but if you add 2 more instances it messes things up somewhat.
Maybe there's something wrong with my approach here, but I don't understand why it works with one enemy but not with many.