So can you only kill them by bumping from one of the northerly directions or by fireball?  Could produce some interesting gameplay, that  
It works like a standard roguelike, you move towards an enemy to attack them.  If you have fire flower (active for limited amount of turns) then you can attack using a throw/fire like mechanic.  Star power will give you limited invincibility for a limited number of turns as well.
@El Barto:  There could be pipes for hidden areas but for now, I'm probably just going to stick to up and down stairs type.  We'll see how much progress I make this week.
The second pipe in the screenshot at the bottom of page 3 is in view, outside Mario's view range for debugging purposes btw.