Battle Unit Zeoth

Players control the Zeoth mecha using jet-powered thrusters to propel the battle unit through the air, and can fire weapons in four directions (left, right, up and down) to destroy Grein enemies. The game includes five stages which include New Age City, the underground base, and the Grein's mechanical command headquarters. The odd-numbered stages are horizontal scrolling stages while the even-numbered stages are short, vertically aligned platform stages. Each stage ends with a boss fight. Players receive points by destroying enemies and clearing stages which contribute to their score, but the high score is not saved and is lost when the Game Boy is turned off.

The Zeoth mecha is equipped by default with a standard Vulcan cannon weapon, and a limited hyper shield, depicted with a meter at the bottom of the screen. The Zeoth can also trigger a hyper bomb to eliminate all Grein enemies on the screen at the cost of two hyper shield meter units. The Zeoth is destroyed if the hyper shield meter is depleted, but the player is offered limitless continues and a chance to start the stage over with a default Zeoth mecha.

Battle Unit Zeoth takes place in the future where mankind is invaded by a race of alien robots known as the Grein. Forty-two years ago, the humans of Earth united to drive out the first invasion of the Grein aliens in a fierce and costly war, but as the Grein retreated, they left behind a secret underground base filled with self-replicating Grein machines.

Ten years after the Earth's victory, the secret Grein base opened and a new attack force decimated the city of New Age. To retaliate, Earth's military has deployed a mecha known as Battle Unit Zeoth, specializing in alien combat. It is the Zeoth's assignment to stop the attack force, go into the Grein secret base, and destroy the mechanical occupants before a new invasion force arrives.

This game was released in Japan under the name "Battle Unit Zeoth". When Jaleco began planning for the US/Europe release they renamed it "Jetpack". This name was later changed back to "Battle Unit Zeoth". It is thought that Jaleco changed the name because they did not think American audiences would buy the game as it sounded too foreign.