In Dead Rising 2: Off The Record for the PC, PS3, and Xbox 360, the Protoman Costume is similar to the Megaman costume from Dead Rising, but with a strong attack that shoots three blasts.
To unlock the Protoman Helmet, you need to defeat Jack at Strip Poker in the Ante Up mission, or in Sandbox Mode. Alternatively you can go to the Arena Security Hall in Sandbox mode at 12:00pm on day one and kill him to get it.
Check out my other guide if you’re looking for the rest of the Protoman Costume pieces.