CosmoTank is a little-known Game Boy game that mixes many different types of play. The player controls the CosmoTank itself, a futuristic armored vehicle with a main cannon and little else. The game takes place across a handful of worlds where the player moves around in a top-down view and defeats the local wildlife in search of dungeons. Once inside, view switches to first person and the player must explore the mazelike tunnels square by square, much like dungeon-crawling role-playing games that use this camera mode. When monsters are encountered, the player must manually aim the cannon and attempt to dispatch them as they circle around the tank. Each dungeon eventually leads to a boss, which when defeated will yield an escape pod. Shooting the pod releases a captured scientist, which helps further the plot and occasionally gives enhancements to the CosmoTank, such as the ability to go over harsh terrain or a charge-up cannon modification that allows the player to concentrate shots for higher damage.
When outside a dungeon, the player can opt to fly to a different world; when doing this, the CosmoTank transforms into a starfighter and the player must navigate a short vertical shooting stage to make it to the next world.
Using a charged cannon blast on a scientist's escape pod will still release him, but it will cause his head on the communication screen to be replaced with a burnt skeleton. The scientist will still be grateful.