To find a patch to fix PC Final Doom TNT level 31, Pharaoh:

Background: In the original commercial release of PC Final
Doom, the TNT/Evilution WAD file contains an error in map
level 31, "Pharaoh", which can prevent further progress in
single-player games: The yellow keycard is missing.

A patch WAD that corrects this error is available from Team
TNT, creators of the Evilution Episode of Final Doom.

Note that this patch file is not required in order to exit
map 31 (see the description of the demo TNT31EX.LMP on the
TntDemos page).  However, the patch is required in order to
access all the keys and all parts of the map.

To acquire and use the patch file:

1. Click to download the file TNT31FIX.ZIP (119,210 bytes).
   This file was originally in the "Bugs & Fixes" section
   of Team TNT's website (http://www.teamtnt.com).
   TNT31FIX.ZIP is a "zipped" (compressed) file which must
   be unzipped before you can use it.
   You may already be using software that unzips downloaded
   files automatically.  If not, you'll need to use WinZIP,
   or the common PC shareware program PKUNZIP.EXE, or some
   other file decompressor that can work with ZIP files.

2. Unzip TNT31FIX.ZIP to create the file TNT31.WAD, then
   copy or move TNT31.WAD to the directory or folder where
   your Final Doom TNT Evilution files are located.  If
   Doom 95 is being used to run Final Doom games, then copy
   the TNT31.WAD file into the Doom95 folder.

3. To play the corrected version of TNT map 31, load the
   TNT31.WAD file when starting up the TNT Episode of Final
   Doom.  (For more information on loading external WADs,
   see http://classicdoom.com/how-wads.htm.)

For more information see Team TNT's textfile on this patch.

Compatibility note: TNT/Evilution save-game files and demos
that were recorded while TNT31.WAD was not loaded may fail
to work later if/when TNT31.WAD is loaded, and vice-versa.
In general, any WAD files that are loaded (or ommitted)
when a given save-game or demo is created, should also be
loaded (or ommitted) when that save-game or demo is later
restored or replayed.