The Grim Adventures of Billy and Mandy (2001)

S6E7 Giant Billy and Mandy All Out Attack

Eager to enjoy classic giant monster films, Billy and Irwin are whisked away by Grim to Japan, where they encounter real-life creatures. They soon find themselves in the midst of an epic clash between Cragorah, a turtle-like beast reminiscent of Gamera, and the three-headed feline menace, Kittirah, echoing Ghidorah. To aid Cragorah, Grim gives Billy a monstrous transformation, turning him into a giant hero akin to Ultraman. Just then, Mandy arrives, furious at their unauthorized adventure. Commanding the formidable Mecha-Gorillasaur, she triumphs over Kittirah and teaches Billy a lesson.