Hey I was playing around with the Super Ninja generator on Seventh Sanctum [link]
which is a great place to get ideas.
What I did was generate about 20 different ninjas and then I took the best parts from each description and this is what I came up with...
This immature ninja is tall and has an angular build. He has oddly elongated arms.His wide eyes are burgandy. He has curly,coffee-colored hair worn in a style that resembles a devil's horns. His outfit includes bell-bottom pants. His outfit includes a lot of belts. He has piercings on his arms. His preferred weapon is a garotte. He can summon a ferret-demon.