On Episode 2 Map 7 (secret level) shoot all of the gargoyle faces once. They will bleed. After that, move to the long, flashing corridor where you encounter two Hell Knights in alcoves. Shoot the wall of the second alcove to reveal a hidden room containing the initials of Tim Willits and Teresa Chasar, along with a raven symbol for the raven levels that they made for Doom 2.
Enter the following codes to unlock the corresponding items:
CHEAT CODE - ITEM (QUANTITY) give all - All Items give health - Health (100) give weapons - All Weapons (All/No Ammo) give ammo - All Ammo (100s/200b&c/50g&s&r) give armor - Body Armor (200) give body armor - Body Armor (+1) god - God Mode notarget - No Target Mode noclip - No Clip Mode give jacket armor - Jacket Armor give blaster - Blaster give shotgun - Shotgun give super shotgun - Super Shotgun give machinegun - Machinegun give chaingun - Chaingun give grenade launcher - Grenade Launcher give rocket launcher - Rocket Launcher give railgun - Railgun give bfg10k - BigFu*kingGun10k give shells - Shells (10) give bullets - Bullets (50) give cells - Cells (50) give grenades - Grenades (5) give rockets - Rockets (5) give slugs - Slugs (10) give quad damage - Quad Damage give invulnerability - Invulnerability give silencer - Silencer give rebreather - Rebreather give environment suit - Environment Suit give ancient head - Ancient Head give adrenaline - Adrenaline give bandolier - Bandolier give ammo pack - Ammo Pack give data cd - Data CD give power cube - Power Cube give pyramid key - Pyramid Key give data spinner - Data Spinner give airstrike marker - AirStrike Marker give blue key - Blue Key give red key - Red Key give security pass - Security Pass give commander's head - Commander's Head give power shield - Power Shield give armor shard - Armor Shard give combat armor - Combat Armor
*The above 8 commands are not activated by the "give all" command.