Z-index of enemy instances...Need Help

Hello all, I'm creating a sidescrolling brawler & I have run into a problem that I can't figure out. I'm hoping one of you may have the answer.

This is how I change z-index based on hero/enemy

<img src="http://www.gamecherry.com/zindex.jpg" border="0" />

Does anyone know how to do this with several enemy instances of the same type? If the enemies are randomly walking around how do I differentiate between them and have them change z-index based on those closest to the bottom of the screen without knowing beforehand how many enemies I may have on the screen at any one time?

Thank you for your time.

You can sort a Z order system using events, without any plugin, let me find the post and show you how.

by the way, it\s very easy to achieve using events.

scirra.com/FORUM/rpg-games-and-the-overlapping-issues_topic51274.html

scirra.com/forum/plugin-isometric-z-ordering-based-on-y_topic46247.html

Thank you. This helped a lot.