Notes:TimeSplitters 2

Codes
G2EB-VKHJ-1JXVF 1XZ1-K0KJ-HMD2E Action Replay code for the GameCube version, which enables the Gothic Tileset for use in the MapMaker. Supposedly the tileset is just called "4" in the menu; its music is called "Gothic Tileset" in the game's soundtrack.

Codes for unused weapons in the GameCube were posted on the GS Central forums years ago, but do not seem to have been archived anywhere.

Hacking
This site has scripts to decompress the PS2 version's PAK (P4CK) files and convert its models (both character and level geometry) to 3ds Max format.

Prototypes
SubDrag documented two demo versions of the game for the PS2. The second one looks almost identical to final, but the first is using TS1 fonts, different terminology, and cuts off before the end of the level so there's probably stuff to be found there. Unfortunately, the names of the discs these came on are not on the site. Apparently there was also an Xbox demo.