One of the bizarre things Teenage Mutant Ninja Turtles Smash-Up did in terms of roster (other than the Rabbids), is instead of having Krang as a playable character, they had an Utrominator. Not many people even knew who the Utrominator was, as they were only seen briefly in the background of one episode of the 2003 series. However, I suppose that only serves to further pay homage to the tradition of having obscure characters in Turtles fighting games.

Utrominator's base was Iron Monger, with his guts carved out with an Xacto knife. The Utrom is from the standard Utrom figure, and the gun arm of ED-209. Everything else is sculpted.