Mickey Moose appears in episode 220 of The Muppet Show. He hangs around backstage and annoys Kermit, especially when his friend Ronald Duck shows up.
Mickey speaks in a John Wayne-style twang, and even makes a reference to a John Wayne film, True Grit. His name is a take on the famous Disney character, Mickey Mouse.
He appears later in episode 519 with Melissa as her Magnetic Moose.