Mega Byogen act as primary antagonists, formed when Byogen faction members infect and possess Element Spirits. This possession warps the spirits into monstrous entities spreading pollution and disease. They originate as small, spherical, bat-like Nano Byogen before possession. Possession drastically mutates their appearance: a dark red body emerges, featuring a tail akin to Byogen generals and a head partially resembling the possessed spirit. If defeated without purification, they crystallize into green-and-red Mega Parts. Starting in episode 20, Byogen generals enhance new Mega Byogen creations by incorporating these Mega Parts, yielding more ferocious, powerful forms with extra abilities. A Sun Element Spirit-powered variant, for instance, grows panels to charge energy and unleash devastating laser beams. By episode 30, Byogen generals develop the advanced Gigabyogen variant. These form by possessing humans or animals instead of Element Spirits, distinguished by a green aura and more humanoid silhouette while retaining core Mega Byogen traits. Defeating them requires the "Final! Healin' Good Shower" attack. Mega Byogen exhibit diverse powers tied to their host Element Spirit: - A Flower Element Spirit enables firing explosive dandelion seeds. - A Wind Element Spirit generates powerful gusts via built-in fans. - A Sound Element Spirit emits noise pollution and, after Mega Part enhancement, neutralizing sound waves. All variants universally spread pollution through energy blasts, lasers, or physical attacks, growing stronger the longer they exist. Purification by Pretty Cure attacks releases the trapped Element Spirit, causing the Mega Byogen to dissipate while uttering "Healin' Goodbye...". Exceptionally potent Mega Byogen can rarely implant parasitic seeds into humans or animals; without swift purification, these seeds risk transforming the host into a new Byogen general. Etymologically, "Byogen" stems from the Japanese word for "pathogen" or "cause of disease," aligning with their role as embodiments of infection and ecological corruption.