I’ve thought about a hour and have no better idea than this:
Evil medieval wizard %evilwizardname% have sent thousands of golems to a good medieval town. Player plays as a good mage killing golems with fireballas and other spells. He can’t kill them all, but he can stop them for a while. This time is needed to evacuate civilians and gain army forces in a rear for battle. Each level is a combination of walls and other town buildings (top-down view, one screen). Straight rows of golems advances from one (or maybe two) screen sides. Golems makes one step per 1-4 seconds, player needs to make a stand against them for a each level defined time. Player can walk around a level using buildings as barricades, he dies when golems hit him at least few times. When level time is over player needs to run to the next level.
I’m going to use HGE 1.81 and Box2D
p.s. sorry for my bad english