Quake 64 

Debug mode 
Enter "QQQQ QQQQ QQQQ QQQQ" as a password and ignore the "Incorrect Password" message.
Then, a "Debug" selection will appear on the option menu.
Level select, all weapons, invincibility, and monster targeting may now be accessed.

No clipping mode 
Enter "NOCLIP" as a password to pass through walls.

Full weapon level passwords 
Enter one of the following passwords to start at the corresponding level with full weapons:

Level Easy/Normal

Realm of Black Magic	?DRY OPFG P3BT VBKX6DRW OPFG T3BR VBJX
The ElderWorld		95RV TPFG QQBT JBJT5SR9 TPFG VQBR JBCT
The NetherWorld		81RV 6PFG RGB5 5BJH41R9 6PFG WGBQ 5BCH
Shub-Niggurath's Pit	79RV 2PFG R7BS SBJF39R9 2PFG W7BQ SBFC
       
 LevelHard/Nightmare

Realm of Black Magic	2DR? OPFG Y3BP VBCXYDR8 OPFG 23BM V3BX 
The ElderWorld		1SR7 TPFG 2QBP JBBTXSR TPFG 3QBM JBFT 
The NetherWorld		01R7 6PFG 0GBN 5BBHW1R5 6PFG 4GBL 5BFH 
Shub-Niggurath's 	PitZ9R7 2PFG 07BN SBBFVR95 2PFG 47BL SBBF 

Level passwords

Level Name		Password

2			Castle of the Damned H40X ZVVB HLBD 74DJ
3			The NecropolisH0P3 2XBN WQ2B NZVK
4			Gloom KeepCWHX CH3B GDB3 14JY
5			The Door to Chthon PQW4 9QVD Y8VY X21M
6			The House of Chthon PL24 XBBT YJLQ 32?6
7			Ziggurat Vertigo6JR3 KDDV 3SLG 9RFT
8			The Ogre CitadelGWY6 7BBB 23BD L4HK
9			The Crypt of DecayB8YN BBBB ZBBB SXR4
10			The Wizard's Manse55R6 0XCJ 2LBR QVV1
11			The Dismal Oubliette 51RZ ?6xQ RGBR NNJH
12			Underearth5XRV SMXP B7BR LP5H
13			Termination Central 5SR9 TPFG VQBR JBCT
14			Vaults of Zin5NRV JF6G CVBR GBFL
15			The Tomb of Terror5JR6 HDXM 2ZBR DPN5
16			Satan's Dark Delight5DR0 HW4N PZ?S 5Y2W
17			Chambers of Torment 49R6 XBBJ 2GBQ 932T
18			The Haunted Halls45RZ ZF32 LZBQ 773R
19			The Tower of Despair41R0 6PFG WGBQ 5BCH
20			The Elder God Shrine4XRV QBFG B3BQ 3BD3
21			The Palace of Hate4SR5 DBBN ZGBQ 1628
22			The Pain Maze4NRV JBBF BRY5 744W
23			Azure Agony4JR5 1BBB 0QBQ X4HX
24			Shub-Niggurath's Pit39R9 2PFG W7BQ SBCF
25			The Nameless City4DR1 4XDD RVBQ VM1B