I've always liked Dyna Bomberman or any of its variants. The concept itself is something that fascinates me. It has a clear goal, you are in a labyrinth and have to make your way out by placing bombs and destroying the walls (destructible) and avoiding enemies (ghosts, blobs, etc).
I believe that this concept can be easily understood by every player from kids to elders. First I looked over the Internet on some existing sprites just to have a visual touch on what I was trying to achieve:
After some brief discussions with Tom (the designer) he came out with some really cool assets and animations.
I'm yet to find a plausible explanations for how the both characters Kil and Mil make these bombs. One possible suggestion would be that Mil is very good at chemistry and they could find the right ingredients to make them on the prehistoric world they were teleported on.