Streets Of Rage 4 — Mr. X Nightmare — an expansion for the old-school side-scrolling beat 'em up Streets of Rage 4. After the events of the original game, our heroes decided to prepare for future threats. Axel, Blaze, and their friends will embark on a special, crazy training session. They will be assisted by Dr. Zan, who developed an artificial intelligence program based on the surviving brain cells of Mister X, capable of simulating any potential danger.