Iggy Koopa, or simply just Iggy, is one of the seven Koopaling children. His shell and hair color vary. He wears glasses and has hair similar to Larry's and Lemmy's.
The artwork for Super Mario Bros. 3 portrayed Iggy with blue-ringed eyes, but some later depictions (including the artwork of Super Mario World) show him with eyes that are swirls instead, possibly to indicate his eccentric personality (this is a common anime/manga convention for eccentrics). Incidentally, Mario & Luigi: Superstar Saga used the original eye design. Iggy is responsible for inventing the robots that the Koopalings use in Yoshi’s Safari. His skills as an inventor are also on display in the Nintendo Adventure Books based on the games. Additionally, in the PC edition of Mario is Missing, Iggy was shown to speak completely in rhyme. Back at Super Mario World, Iggy used to have white hair and a blue shell. The last game that he had a rainbow mohawk was in Mario is Missing!, but he now has green, tree-like hair.
Iggy is the fourth boss of the game, in Giant Land. To beat him, the player must use the usual three-jump routine to defeat him while avoiding his magic blasts. His sprite has white hair and a blue shell.
Iggy is the first boss in Super Mario World, in World 1, Yoshi's Island. His only attack is throwing fireballs. To beat him, Mario must jump on his head or throw fireballs at him to knock him back until he falls in the lava below.
Iggy is the sixth boss in this game. He rides a giant Mecha-Blooper. The first weak spots are the tentacles on top. After you destroy them, the Mecha-Blooper dives. You must destroy the tentacles when they come out of the water. After you beat it, it will reveal Iggy, clinging to a piece of debris floating in the ocean. When he is defeated, he gives up the Pearl Gem.
Iggy is the first boss of Bowser's Castle. Upon reaching his room, he spins rapidly around Mario and Luigi, causing them to get dizzy. The player must figure out the mixed-up directions the Bros move in to dodge fire racing around on the ground, or else they must start over. At the end is Iggy, who will fight them if they reach him. He can spit fireballs that can be countered with the Hammer. He also has a rapid spin attack; if he is not hammered enough or in time, he will damage the Bros.
Iggy appears in New Super Mario Bros. Wii as the fifth boss. At his tower, he will gasp in sarcastic terror and spank himself, his signature taunt. He will then fire green magic flames and bounce around on three moving platforms. He must be stomped on three times to be defeated. In his Castle battle, he will ride in a Chain Chomp vehicle pulled by a Chain Chomp made giant by Kamek's magic. Mario has to prevent getting hit by the Chomp and Iggy's green fireballs. After three stomps, he is defeated. Iggy now has solid yellow-green hair and a yellow-green shell.
Iggy's appears in his battle riding another Chain Chomp vehicle (the Chomp remains normal-sized) in World 2 of New Super Mario Bros. 2. He also appears in the Castles of Worlds 6 and 9, along with the rest of the Koopalings, in their giant Clown Car.
Iggy, instead of spanking himself, will make lava rise underneath him and Mario. He will slide into pipes and come out of others, sometimes walking on the ceiling. His magic consists of not only green magic flames but also red ones with skull patterns. When the red flames hit the lava, they spawn Magmaarghs.
Iggy is a placeable enemy in Super Mario Maker 2, as part of update 3.0, the final major update. He can run forward and backward. He has to be stomped on three times like other Koopalings, if the player gives him wings, he will act in the same way as in New Super Mario Bros. Wii.
Iggy is a playable character in Mario Kart Tour. He must be unlockable and is a normal character.
Iggy is considered as demented and extremely smart but is rather weak compared to the other Koopalings. He enjoys laughing maniacally at the player during fights. He is even stated as "The Demented Koopa" in Super Mario World.
In the cartoons, he was called Hop Koopa (Lemmy, his brother, was named Hip, a play on the urban music genre hip hop). In the cartoons, Hip and Hop are twins, as well as the youngest of the Koopalings. Though, the cartoons are not part of the series canon. Hop’s overbite and non-swirling eyes are the only significant ways in which he differs from Lemmy. In Super Mario World, his hair was matched by the artwork of him in-game.
Super Mario Bros. (film)
In the Super Mario Bros. (film), one of King Koopa’s cousins is named Iggy.
Iggy was named after James Newell Osterberg Jr., better known by his stage name, Iggy Pop, who is the lead singer for the American rock band, the Stooges. 
Out of all the Koopalings, in New Super Mario Bros. Wii, Iggy has changed the most from the old games, as he is now taller, thinner, and his hair color has changed from rainbow to solid green and is styled somewhat like the base of a flower. His shell is still green like before, though it is more of a lighter shade and is the same color as his new hair-do.