From the Super Mario Wiki
The Pipe Creatures are two giant characters in the TV series The Adventures of Super Mario Bros. 3 where they appear in the episode "A Toadally Magical Adventure". Originally, they were normal pipes, but Toad transformed them into live beings with the Wizard King of the West's wand. At first they were peaceful, as Toad only instructed them to make noises out of their pipe holes, but he kept bossing them around to make louder and faster noises. This got them angry, so they stole the wand from Toad and brought to life a couple of blocks to terrorize Toad.
King Koopa later came and saw that the Pipe Creatures had the wand. King Koopa then instructed some Boomerang Bros. to get the wand. The Pipe Creatures dodged the boomerangs with ease and laughed, but were caught off guard when they came back, and they lost the wand. Koopa then froze them with the wand.
Later, Bully Koopa was making the Pipe Creatures play a game of catch with the Mario Bros. and Toad as the balls. Cheatsy Koopa made a giant Nipper Plant attack Mario, but the blue Pipe Creature was hit instead. Mario then wrenched the purple creature's arm off to free Toad. However, the blue one caught Mario again, and was then destroyed after Mario turned into Raccoon Mario.