Changing the draw layer priority of objects?

how do I change the layer priority of objects? Like, if I add a monster thats a puddle, I want it to hurt the player when he walks over it. That part works, but the puddle looks like it drawn on top. How can I set it so the puddle is drawn behind the player?

You could try this modificattion : http://nesmakers.com/viewtopic.php?f=40&t=2455&p=15394
This make the Player always on the first prority.