You can stack enemies on top of each
other to make mountains of enemies; you can also add wings to some enemies to let them fly, float, or bounce, or you can make them extra big by giving them a mushroom; you can put enemies or powerups in pipes so that they respawn whenever they get killed / disappear, put them in
breakable blocks / coin boxes to give players a surprise, or combine certain
objects and enemies together for all new challenges.