Koopa trash

Koopa trash is waste left behind in Brooklyn by King Koopa and the Koopa Kids in The Adventures of Super Mario Bros 3 episode "Recycled Koopa". The effect the garbage has in the Real World is that it mutates humans who come in contact with it into a Koopa Zombie, other animals into Koopa's minions (e.g. seagulls into Paragoombas and fish into Spiny Cheep-Cheeps), and even statues into reasonable facsimiles of the evil king himself, such as the Statue of Liberty. Staying away from the garbage or cleaning up the garbage results in the victim being changed back to normal.

History
After King Koopa demands the Koopa Kids to clean up the garbage from his castle, they send it to Princess Toadstool's castle garden using a Warp Pipe. Mario, Luigi, Toad, and Princess Toadstool go to King Koopa's castle and steal Hip's magic wand and use it to send the garbage back, taking the wand with it in the process. Back at the Mushroom Castle, Mario uses Luigi's Plumber's Periscope and spots several Sledge Brothers dumping the garbage down another Warp Pipe leading to another world and decide to follow the garbage's path. They hide in the trash boxes and get thrown down the pipe. They find themselves back in Brooklyn, but covered by the Koopa trash. The brothers witness the people of Brooklyn being mutated into Koopa Zombies and attempt to clean up the garbage. When the Koopa Kids bring the powers the garbage has on the Real World to their father's attention, Koopa brings his Doom Ship to the Real World and dumps more trash to mutate the rest of New York City and the Real World, as well as for the mutated victims to use as ammunition against the brothers. It is after Mario begins to mutate into a Koopa Zombie himself that he and Luigi decide magic is not really working to clear out the garbage and build a machine known as the Trash Smasher to clean it up. As Koopa continues dumping more garbage on the city with his Crud Cannon, a stray pile from the cannon lands on Mario, completing his mutation shortly after he and Luigi are making the final touches to the Trash Smasher. With the Trash Smasher, Luigi successfully cleans up all the trash, restoring Mario and the entire city back to normal. King Koopa tries to dump more garbage, but Mario and Luigi make the Trash Smasher flight-capable and fly it close enough to the Doom Ship to suck up the garbage before it reaches the ground and chase Koopa out of the city.