Quake 2
Twists level:

Enter FBBC VBBB FBBC VBF7 as a password. This is deathmatch level with a 1:40 time limit and rocket launcher. 

Deathmatch level:
Enter FVBS LBBB 7VBC 3BGB as a password to play in a level similar to "Twists", but with a greater challenge. 

Additional costume colors:
Enter S3TC 00LC 0L0R S??? as a password. 
Information in this section was contributed by poky1. 

Low gravity in multi-player mode:
Enter S3TL 0WGR V1TY ???? as a password. 

Unlimited ammunition in multi-player mode: 
Enter S3T1 NF1N 1T3S H0TS as a password. Note: This code also allows higher jumps.
Information in this section was contributed by JVGART5 and poky1. 

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Level passwords:
To access the password screen, choose "Load Game", then press B when the list of saved games appears.

Level Password 
2 PGBR VK?B 65BH Y3HD 
3 1KLS DN5H 7NBF DWRQ 
4 2KLR SDRY ?VV4 YQ8X 
5 VK3T 7LFC 94B7 D3R3 
6 WK3H QNBW NLV5 XGL3 
7 TK7P 6LLP KWGY XD4V 
8 ST0N QPX4 2WGY JXTS 
9 R??P 7NY4 2WGX 99TX 
10 Q??K BBBV NBQ1 7GCV 
11 P64? ZM5B ?BM0 5YH6 
12 N664 SQ63 XB?K B7LF 
13 M682 M7QT 1215 8098 
14 L669 H8MD G8XB JNYV 
15 K681 X8CL H01K 1PF5 
16 J6?0 BT5M NRZ2 QXLL 
17 H6?0 XXFW PHV1 77P4 
18 G6?9 GYMK RWNK SMSL 
19 F6Y3 WXQK CHD0 8K4D