Blue SpongeBob is an alternate universe version of SpongeBob SquarePants, who exists in a universe where SpongeBob is blue instead of yellow. He may also exist in the same universe as Green Patrick or Plaid Patrick.
In both appearances, he looks exactly like SpongeBob, except he is blue, has black freckles, and a pink chin.
In Bikini Bottom 2, he also wears a green and yellow horizontal striped headband.
He is the second alternate universe character that SpongeBob summons to the Bikini Bottom 2 universe after Sandy Evil-Cheeks.
He also appears when he brings the next three, which are Green Patrick, Plaid Patrick, and Patrick Star.
He later appears at the end in the crowd of alternate universe characters. He appears next to Werewolf Mermaid Man and Werewolf Barnacle Boy. He is also in front of Patrick Star and Red SpongeBob.