Gavin Koopa is Tara Koopa's best friend. He looks like Iggy but has green hair like larry's, two teeth and green shell.
Super Mario Bros 3
Gavin dressed up as Iggy and stole the Grassland King's magic wand. Then he gave it to the real Iggy.
Super Mario World
Gavin made the walls close in the Morton battle and tried to make Morton black with the shades. Then Morton knocked him out the window.
Mario is Missing!
Gavin doesn't appear in the game, but Larry mentions him.
Gavin dresses up as Iggy in the final battle, because the real Iggy actually was sick with the flu.
Gavin was also stuffed with Iggy in the Robo-Blooper without being seen.
Mario and Luigi:Superstar Saga
Gavin dressed up as Larry, because the same thing that happened to Lemmy also happened to Larry.