Secret Gamerpics:To unlock a Gamerpic of a demon, beat a level on Nightmare difficulty. To unlock a Gamerpic of a Doom Marine, get a 100% kill rating on a level on Hurt Me Plenty or higher difficulty.Level 2: Secret room:Go to the dark section inside the red door area. Punch the wall behind the green armor at the back of the dark area. This will lead into a secret section.Run faster:While running keep touching a wall to move faster. Nightmare mode:Cheat codes cannot be used in nightmare mode. It is just like the regular game, except the monsters are stronger and harder to kill. Enemies will keep appearing non-stop on each level; you have to try and get to the end before more appear.Achievements:ACHIEVEMENT – HOW TO UNLOCKNeophyte (20 points) – Beat any level.Episode One (25 points) – Beat Episode 1 on the “Hurt Me Plenty” or higher difficulty.Episode Two (25 points) – Beat Episode 2 on the “Hurt Me Plenty” or higher difficulty.Episode Three (25 points) – Beat Episode 3 on the “Hurt Me Plenty” or higher difficulty.Episode Four (25 points) – Beat Episode 4 on the “Hurt Me Plenty” or higher difficulty.Rampage (35 points) – Beat all levels on UltraViolent mode.Nightmare (10 points) – Win a Nightmare level in single player.Rookie (10 points) – Get 50 kills on Xbox Live.Destroyer (10 points) – Get 100 kills on Xbox Live.Scout (5 points) – Find a secret area of a map.Hoarder (5 points) – Find all items in level.Clean Slate (5 points) – Kill all monsters in a level on the “Hurt Me Plenty” or higher difficulty.