In the first episode of The Adventures of Super Mario Bros 3, the Ninja Koopas are sent to dispatch a giant mushroom man. When they get there they are the same size as the giant.
I can't remember how they became giant themselves, if it was explained at all?
This was addressed in the Season 3 premier episode Sneaky Lying Cheating Giant Ninja Koopas. King Koopa uses magic on his henchmen to make them large.
A panicking Bully is suddenly pushed forward by Kootie Pie Koopa. As King Koopa prepares to zap the protesting Bully with his wand, he orders Big Mouth, Cheatsy and Kooky von Koopa to step forward. As Kootie Pie, Hip and Hop Koopa back away, King Koopa zaps Bully, Cheatsy, Kooky and Big Mouth with his wand, turning them gigantic and inexplicably giving them weapons and ninja costumes. King Koopa then commands his colossal children to go out and kidnap Prince Hugo so he can conquer Giant Land.
