In Dead Rising 2: Off The Record for the PC, PS3, and Xbox 360, the Ninja Costume can make you quite a bit more stealthy. While wearing any part of the costume, you will be less detectable by regular zombies.
The Ninja Hood can be found in Royal Flush Mall. Climb on top of the phone booth on the second level and climb up onto the next ledge. Run to the end of the ledge and jump to the next ledge. Turn around and jump and climb up to the flower box, then jump to the next ledge. Walk into one of the open windows and you’ll find the Ninja Hood sitting on a box on your left.
Check out my other guide if you’re looking for the rest of the pieces to the Ninja Costume.