At the console type 'spawn X' (without the quotes and replace X with the corresponding character type) to spawn that character. For example, to spawn an Assassin, type 'spawn enemies_ak_assassin'. Specific enemies can only be spawned into the current level if they already appear somewhere in the level.
Spawn an Assassin: Spawn enemies_ak_assassin
Spawn a Flamethrower Trooper: Spawn enemies_ak_flame_trooper
Spawn a Heavy Trooper: Spawn enemies_ak_heavy_trooper
Spawn a Scribe (Magic user): Spawn enemies_scribe
Spawn a Sniffer (Mutant): Spawn enemies_sniffer
Spawn a Rocket Trooper with a Jetpack: Spawn enemies_ak_rocket_trooper
Spawn a Red Despoiled (Flaming Skeleton): Spawn enemies_despoiled_red
Spawn a Green Despoiled (Flaming Skeleton): Spawn enemies_despoiled_green
Spawn an Altered (Giant, Invincible Mutant): Spawn enemies_altered
Spawn a Wehrmacht Officer Armed with an MP40 SMG: Spawn enemies_wehrmacht_officer
Spawn a Wehrmacht Sniper Armed with a Sniper Rifle: Spawn enemies_wehrmacht_sniper
Spawn a Wehrmacht Soldier Armed with an MP40 SMG: Spawn enemies_wehrmacht_infantry_mp40
Spawn an SS officer Armed with an MP43 Assault Rifle: Spawn enemies_SS_officer
Spawn an SS Soldier Armed with an MP43 Assault Rifle: Spawn enemies_SS_sentry
Spawn a Blonde Haired Elite Guard Armed with a Dagger: Spawn enemies_elite_guard
Spawn a Brown Haired Elite Guard Armed with a Whip: Spawn enemies_elite_guard_02
Spawn a Wehrmacht Soldier Armed with a Kar98 Rifle (Map will crash if this enemy type present in the level): Spawn enemies_wehrmacht_infantry
Spawn a Friendly Kreisau Soldier Armed with an MP40 SMG (Valid characters are 01 to 05): Spawn allies_kreisau_soldier_01
Spawn Friendly Erik Engle Armed with an MP40 SMG (Has more Health than a basic Kreisau Soldier): Spawn allies_kreisau_erik
When you have completed the game once you will be able to press 'Esc', followed by 'Options', 'Game Options' and 'Cheat Menu' to get All Weapons and Veil Powers, Infinite Money and Pumpkin Heads mode. Using these cheats though will disable Achievements and Trophies.
When you have reached level 4 push the hidden walls inside the bunker in the correct order and you will find one of the ghosts from Pac Man. The code which needs to be entered can be found on the opposite-facing wall and is there for about 3 seconds, you will also see a telephone number which tells you to say a word to the receiver.