Petasos is a Negamonster sent by Neflite to gather energy for the Negaverse. She attacks by controlling animals to turn them evil, extending vines from her hair to wrap around her enemies, and throwing bombs that exploded into vines that would wrap around the enemy. She appeared in Sailor Moon Episode 12, An Unnatural Phenomena.
Her essence was implanted inside a man named Mr. Baxter by Neflite. Once his energy reached its highest point, she awakened and began to steal energy from him. She battled Sailor Moon and Sailor Mercury, and trapped them with her vines, but was stopped by Sailor Mars. After the arrival of Tuxedo Mask, Sailor Moon destroyed Petasos with Moon Tiara Magic.
Her name is derived from the word petal, as she is a plantlike monster who uses vines as a weapon.
Name Source: From Greek "petasos" for a broad leaf.