Stripèd Green Rabbit
From Homestar Runner Wiki
The Stripèd Green Rabbit grew out of a hypothetical suggestion by Strong Bad. In The Cheat's Powered by The Cheat Flash cartoon "New Boots", The Cheat gives Strong Bad purple boxing gloves and shows him wearing underwear. Strong Bad objects that The Cheat didn't do any fact checking, asking how The Cheat would appreciate being represented as "a stripèd green rabbit... with two butts". At this mention, an Easter egg made the animal visible.
The Striped Green Rabbit appeared in the Hip Hop Dance music video immediately following "New Boots", but has never been seen since (except in the form of a fan-made pumpkin carving featured in Punkin Show).