From WiKirby, your independent source of Kirby knowledge.
Moonja is an enemy that debuted in Kirby's Return to Dream Land. It yields the Ninja ability when swallowed.
Moonja resembles Kirby in physique, but bears somewhat more defined white hands and feet, with a yellow face and purple ninja garb. It phases in to ambush Kirby, hopping in many different fashions to avoid getting hit, and tosses shurikens. It will also attempt to phase out and warp back in behind Kirby to get the jump on him. Moonja has a fair amount of health, but cannot stand up to Kirby's Inhale, or a good pummeling with any other attack.
Moonja also appears in Kirby: Triple Deluxe, unaltered from its previous appearance. It is capable of traveling between the foreground and background when it vanishes. It also appears in Kirby: Planet Robobot, serving the same purpose.