Mac

 Despite being a lot less fish–like than his colleagues, Mac is just as dumb as them. He will eagerly do anything for food or something to chew on, which more often than not lands him in some hot water.

On top of that, he has a tendency to get lost, usually winding up on the wrong map or worse, on Inkling territory when he does. The bobber on his collar is supposed to help others find him and warm Inklings of his approach.