Helio, originally known as Yellow Belly, is a boss in the videogame Wario Land 3.
Helio looks like a balloon with arrowheads on his arms. Apparently, there is a toxin that turns Wario into Puffy Wario on the tips of the arrowheads.
Helio is easily frustrated, as portrayed in the game. In the boss battle, Wario must do a Ground Pound on his head to release an accordion-shaped device from his mouth. Then, Wario must do a ground pound on that in order to inflate Helio, and the entire pattern must be repeated twice more in order for the boss to be defeated.
Helio, like many other Wario Land 3 characters, later appeared in Dr. Mario 64. He patrols the sky, watching for ongoers.
In Dr. Mario's story, he is angered by Dr. Mario and Wario while they chase Mad Scienstein to get the Megavitamins. Because of this, he pops Wario, and Dr. Mario, who's just behind Wario, has to beat him in a match. He is not battled by Wario, and is instead replaced by Lumpy in Wario's story.