Giant Poop Koopa looks like Roy, but has poop all over him.
Super Mario Bros. 3
Giant Poop doesn't appear in Super Mario Bros. 3, but Roy says that he pooped all over him, making him look like a poopy goomba. Roy says that goombas (escpecially poopy ones) are so dumb that they are stupider that Stupid von Koopa and Epic Fail Koopa.
Super Mario World
Giant Poop poops all over Mario, making him look like the really wierd sprite of Mario from Super Mario World. He makes Reznor spit poopballs instead of fireballs in the outtakes. Then Poopsie Chucklebutt stomps Stupid Fart into a flatty pancake and eats him with syrup. ("Stay on topic!" shouted Ludwig)
Mario is Missing!
Giant Poop poops all over Antarctica, making the King Penguin chicks look brown with poop. Then Luigi comes, and Giant Poop poops all over Luigi. And Yoshi said "Argh! Why did you poop on Luigi?" and stuffed Giant Poop into a bell made of poop. And the Tyrannosaurus Rex said "Argh! No stuffing Giant Poop into a poopy bell!"
Giant Poop doesn't appear in this game, but Roy mentions him.
Giant Poop pooped all over Mario, Luigi, the gems, Princess Peach, and Yoshi.
Mario & Luigi: Superstar Saga
Giant Poop went and pooped on Cackletta and Bowser, so they spanked Giant Poop and flushed him down the toilet.
Super Princess Peach
Giant Poop pooped yellow poop all over Perry.
New Super Mario Bros. Wii Giant Poop pooped all over the cake, the title screen, the TV the players are watching, the final Bowser battle, and the credits.