Mick is one of the Rat Bandits that is a part of the "Splinter Group" optional mission. Mick is the last bandit that comes out when you place the pizza on the table, then disappears once his health gets to halfway. Once he disappears, he will reappear with the other three bandits.
Mick is an Easter Egg of Michelangelo from the Teenage Mutant Ninja Turtles.