Chimeras are three-headed mythological beasts. Each of their heads are of different types of animals such as birds and snakes.
Yellow & Green, his father, debuted & only appeared in "Samurai Vac" as the semifinal main antagonists.
In said episode, one of the Chimeras, Yellow, was causing destruction in the city. Samurai Vac tried to fight it off, but Jenny managed to defeat Yellow himself. With a seismic kick, Jenny sent Yellow flying.
After a while, Yellow (now looking blue) managed to return with another much larger Chimera & his father, Green. Jenny was eaten and spat out by Green, leaving only Samurai Vac to stop the 2 Chimeras. Vac used his vacuum abilities to defeat Green. This caused the Tokyokkos to laugh at the 2 Chimeras & Green (now with his main head & butt burnt by his snake-headed tail) to leave Tokyo forever in shame, while Yellow, being shocked by Jenny, Samurai Vac, & the bad occurrence on his father, just did the same.
Yellow & his father, Green are the semifinal villains of the entire series.