Yamikage

Yamikage (which is Japanese for Dark Shadow) is a villain in the Kirby: Right Back at Ya! anime. He was once a member of the Ninja Special Forces of the Galaxy Soldier Army, but eventually defected to the side of the Emperor of Darkness, Nightmare. That fact is proven when he is seen riding on top of the head of a massive silver dragon, which is just one of Nightmare's kaiju-esque monsters seen in Meta Knight's flashbacks.

Years later, King Dedede purchased Yamikage to help him steal back Benikage's "failing" report card - which everyone thought was a ninja scroll! Benikage's curiosity almost gets him killed when he challenges Yamikage, but luckily, Kirby steps in to save the day as Ninja Kirby, and quickly overpowers Yamikage. Afterwards, Yamikage retreats, and is last seen running through the woods, promising revenge on both Kirby and Meta Knight. Strangely enough, he never comes back afterwards, so therefore he remains a mystery.

Physical Appearance
Yamikage appears to be shaped like an upside-down egg with sunken-in red eyes and a scar on his right eye. He wears black ninja clothing and has a brown ponytail, and wears a katana's sheath on his back. Interestingly, Yamikage closely resembles Bio Spark.