Zombies Hate Aliens!

The zombies had an agreement with the aliens, but then suddenly the aliens plan to use weapons which melt human brains. Since this is incompatible with the zombies' nutrition needs, this means war! The setup: on the left of the screen is the zombie headquarters, flying saucers enter from the right and try to crash into the building and the player controls a catapult on the ground. The catapult can be moved both in position (left or right) and fire angle. The goal of every level is to bring the alien's health bar (decreases from kills) to zero before the HQ health bar (decreases from crashes) runs out. Additionally every kill rewards money which can be instantly used to buy health, ammo or weapon upgrades. Over the course of the 40 levels, both the zombies and the aliens gear up: the zombies get new projectiles, e.g. a balloon which go with the wind, and the aliens receive abilities like teleportation or bombs.