All keys (special password):-  Enter KNGHTSFR as a password.

All maps (special password):-  Enter LMSPLLNG as a password.

All weapons (special password):-  Enter THRBLDNS as a password.

Unlimited ammunition (special password):-  Enter NDCRSDRT as a password.

Unlimited health (special password):-  Enter HLGNDSBR as a password.

Level skip (special password):-  Enter NFTRWLLH as a password. Go to the map screen, and press Select to advance to the next level. 

Sound effects test (special password):-  Enter CRSDR as a password. Enter the game options menu, then set "Sound FX" to "Off", then back "On" to hear a random sound.

God mode (special password):-  Enter S_X_N as a password. Note "_" indicates a space. This code activates unlimited health, all weapons, all keys, unlimited ammunition, all maps, and the level skip features.

Cheat mode:-  Enter NRYRDDS as a password. Note: This code disables all the "special password" codes. The following cheat mode passwords may now be entered.

All keys: KEYS
All maps: MAPS
All weapons: WEAPONS
Unlimited ammunition: AMMO
Unlimited health: HEALTH
Level skip: SKIP
Disable cheat mode and enable "special password" codes: PWORD
Sound effects test: SFX TEST
God mode: ALL 

Additionally, the following passwords can be entered in cheat mode to advance to the corresponding level and difficulty. 

Level 2, Easy Mode: A
Level 3, Easy Mode: B
Level 4, Easy Mode: C
Level 5, Easy Mode: D
Level 6, Easy Mode: E
Level 7, Easy Mode: F
Level 8, Easy Mode: G
Level 9, Easy Mode: H
Level 10, Easy Mode: I
Level 11, Easy Mode: J
Level 12, Easy Mode: K
Level 13, Easy Mode: L
Level 14, Easy Mode: M
Level 15, Easy Mode: N
View End Credits, Easy Mode: O
Level 2, Medium Mode: AA
Level 3, Medium Mode: BB
Level 4, Medium Mode: CC
Level 5, Medium Mode: DD
Level 6, Medium Mode: EE
Level 7, Medium Mode: FF
Level 8, Medium Mode: GG
Level 9, Medium Mode: HH
Level 10, Medium Mode: II
Level 11, Medium Mode: JJ
Level 12, Medium Mode: KK
Level 13, Medium Mode: LL
Level 14, Medium Mode: MM
Level 15, Medium Mode: NN
View End Credits, Medium Mode: OO
Level 2, Hard Mode: AAA
Level 3, Hard Mode: BBB
Level 4, Hard Mode: CCC
Level 5, Hard Mode: DDD
Level 6, Hard Mode: EEE
Level 7, Hard Mode: FFF
Level 8, Hard Mode: GGG
Level 9, Hard Mode: HHH
Level 10, Hard Mode: III
Level 11, Hard Mode: JJJ
Level 12, Hard Mode: KKK
Level 13, Hard Mode: LLL
Level 14, Hard Mode: MMM
Level 15, Hard Mode: NNN
View End Credits, Hard Mode`OOO 

Level Easy Medium Hard 

2 CRSDRPLS VWHTSRGH LDNHGHNT 
3 TKMWTHYB TCRSDRLR DBYFTHND 
4 TTLLSFRT DFRLMWTH CSSRCNHT 
5 STCRSTRD LLYRMGHT HNSWLLSN 
6 NTLVMLNW WRMRCHNG TSTRSTLR 
7 NTTRDTNY TLNDFRFR STNDRDSW 
8 RQSTMWTN MHMNNCNS LLRSCRSS 
9 GTSTNDBY YWHLLRTR LNDTBTTL 
10 YRSDTFGH NFRCHRSN SRCNHRDS 
1 TWTHYVRS DMSSKWLL WFLLWRWR 
12 THYRCLLN TKRRVNGN RRKNGNWR 
13 GHVTBTHR PGNFRMTF DNTFGHTW 
14 HLYLNDHS STWCHRST CRRYSGNF 
15 TBFRFGHT NSRCMNGW CRSSWRLR 
End GDFGHTBL THSWRDSH DSFNGLND