Levels 1-5 and 10 are not new levels -- they're from the original TTF. To access the first of the 3 new levels, run debug.bat to enable cheats and warp to level 16. It is possible to get to the alternate secret levels from level 1 without cheats, but to do so you will have to solve some rather difficult puzzles. (Hint: There are two trigger switches on Level 1. The first that you will find toggles which pushwall type you can open, and the other makes the secret elevator take you to level 16 rather than level 10. Also, the first of the pushwalls is in the purple-stone corridor that leads to the blue key.)

At the very beginning of level 16, you are in a room with suits of armor. One of the suits contains a chaingun -- to get it, press the Use key on the suit and remove the chaingun that appears to the left. This chaingun will upgrade your chaingun and make it more powerful.

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