A 1990 Shoot 'em up for the NES by Compile, Gun-Nac is full of murderous robot bunnies firing explosive carrots, giant cat statues, and a bank level where you're attacked by gold coins. The game starts out being very fun and pretty easy, until AREA-7 and 8, where the difficulty ramps up quite a bit. Still, the game has infinite continues, which makes it doable.
