BioHazard Ninja is a character who first appeared in Illness. He was the last enemy that Princess Bubblegum had to fight in order to reach the cure for Cinnamon Bun's disease.
BioHazard Ninja wears a dark-green ninja suit with lighter-green shoes, gloves and hat. He has glowing green eyes and is never seen without his BioHazard Shurikens.
BioHazard Ninja is a master ninja who is very good in hand-on-hand combat. He mostly uses his BioHazard Shurikens which also return when thrown. When his shurikens hit someone it sends some poison into the body, as explained by him.