ninjas are fast, deadly, have cool weapons (everyone wants a katana its on everyones top 50 things to have list), and being called ninja is a compliment cause thats how cool they are (whats up mah ninja) unicorns are also fast, can be deadly (unicorns on drugs), they are horses with horns ( you know if you had a horse it would be 50x better with a pointy horn, and they shoot rainbows and sunshine all over the place, and they are frickin mythical beasts of epicness WHO WHOULD WIN ANSWER THY QUESTION PEOPLE
The ninja would throw a shrewkin which would only spin into and be deflected by the horn, then the unicorn would ride a rainbow at light speed piercing the ninja right through the face with tremendous power. Unicorn is the champion hands down.
Huh guys, I dunno. I must agree that their powers combined would be better than anything a ninja or a unicorn could do by itself. I could imagine a ninja upon a majestic unicorn, slashing through an opposing army merrily.
There would be rainbows and stuff shooting out everywhere as the ninja killed everybody.