The Bootleg Costume is a costume currently sold at the Pirate Ship. Bootleg pets are poorly drawn versions of their original counterparts. A bootleg is something that is made, distributed, or sold illegally, sticking with the nature of pirates. This is also true for video games: bootleg games are sold in the black market. Defrosted and Pikaboo are bootlegged counterparts to Frozen and Pikachu.
Also, it was going to be an April Fools' prank, but Ian ran out of time to make it happen.