
The important byte is the ninth one, "17". These five pairs of bytes respectively describe its x-coordinate, its y-coordinate, its angle, its thing type and - most importantly - its flags. If you've got a legitimate unpatched version of TNT.WAD, the ten byes starting at 0x49483C should read as follows in a hex editor: With a bit of detective work and a map editor, I found out that the yellow key is thing 470 and that its entry in map31's thing list begins at byte 0x49483C (decimal 4802620) in the IWAD.


The problem is that the yellow key has incorrectly been flagged as "multiplayer only". All you'll need is a hex editor (if you've not got one, google it - there are various freeware ones kicking around the net.)

There's another, very simple way to patch the IWAD without causing utilities etc.
