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Sprites for an unfinished dragon boss can be found in the game's data. This boss has no working code and cannot be activated in-game.
Contributed by MehDeletingLater
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An unfinished boss resembling a cowboy rabbit can be found in the game's data. This boss has an unused animation depicting it firing its gun. According to an early sketch of the game's cover art by Hideyuki Suganami, this boss was named "Lambda Bunny".
Contributed by MehDeletingLater
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An unused boss resembling a hand can be found in the game's data and can be fought in Stage 13 through hacking. This boss was featured in pre-release screenshots of the game, and was named "Love Penguin".
Contributed by MehDeletingLater
Seven Force, a boss from Gunstar Heroes that appears in this game as the boss of the Underground Mine stage, was originally intended to have two extra forms: Harpy Force and Nemesis Force. These forms were never finished due to time constraints, but voice clips of the game's announcer saying each form's name can be found in the Voice Test, and their idle sprites can be found in the game's data.
Contributed by MehDeletingLater