PlayCo Armboy

Backstory
The PlayCo Armboy is a mechanical arm added to the user's arm to win a game of arm wrestling, albeit unfairly. It is featured in the episode, "Over the Top". It was used by Rigby to cheat against Skips at arm wrestling as a prank, until the latter later found out about it when Mordecai told him. In the final game of arm wrestling, Skips pulls the Armboy off of Rigby's arm and accidentally kills him. Later, Skips uses the Armboy to beat Death in a game of arm wrestling to save Rigby's life. Skips told Rigby that he only cheated to save his life, and then Skips told him never to cheat again.

In the Fighters of Lapis series
The PlayCo Armboy appears as an item. It is worn on one of the user's arms/appendages. This boosts their grabs and punches, having atomic effects with them.