Koops is a shy Koopa Troopa from Petalburg, and the second partner to join Mario's party in the game Paper Mario: The Thousand-Year Door, after Goombella. His left eyelid is half-closed, and he wears a bandage on his nose, a light-blue hoodie, blue pants, and white shoes. Very much like Kooper from the original Paper Mario, Koops can retreat into his shell and use it as a weapon against foes, and Mario can also launch him at switches or distant objects to hit them or retrieve them. However, he differs from Kooper in that Mario can hold Koops's shell in place. He has a girlfriend named Koopie Koo and a father named Koopley. His name is a portmanteau of "Koopa" and "oops", an exclamation of clumsiness (Koops being clumsy); it is also a real surname.
He makes a cameo in SMG4: Mario Preschool.