The Demon Frog (Devil Frog in Japanese) is the major antagonist and a petite yet powerful monster ordered by King Dedede (before Heavy Anaconda) in the Kirby: Right Back at Ya! episode, Frog Wild.
When Kirby gets possessed by the Demon frog, he greatly resembles his normal self, but he has bat wings on his back and his eyes get longer and sunken in. The eyes also begin to glow dark red. He is also commonly sneering while possessed too, making evil laughs. Dedede certainly changes much more than Kirby does when he's possessed by the Demon Frog. His muscles grow to epic proportions and his lower body gets leaner. His robes rip due to the dramatic size increase and he now has small bat wing-shaped markings on his chest. Like Kirby, Dedede's eyes begin glow red when possessed, but unlike Kirby he also grows small fangs. The possessed Dedede easily pummeled Kirby like a hammer, but just as the posessed Dedede was about to deliver the final blow to Kirby, the battle was soon interrupted by another monster that comes out from hiding called Heavy Anaconda that Dedede ordered from Nightmare Enterprises. The Demon Frog eventually met its demise when it got devoured by the huge brown snake, freeing Dedede in the process from its control.
The Demon Frog is a small, round green frog with a yellow underbelly and small purple bat-like wings. It has large orange eyes and purple markings all around its body. Whenever the frog possesses people, the victim gains glowing red eyes, menacing facial expressions, and sometimes even a change in body type.