First off, Happy New Year!

I fiddled around with these games about a year ago (could be longer than that), and made some codes for the first game. Unfortunately, I don't have the retail discs anymore. My knowledge on defeating the LibCrypt is non-existent. But the purpose of this pm was to let you know that the button cheats might work on your demos. The cheats for the first game doesn't work on mines (demo found on the Pizza Hut Demo Disc). I also saw some codes ported from mines that verify they work on the PlayStation Underground Jampack Winter '98 demo. 

Your Medievil demo is also older than the Pizza Hut one. It was built on 9/17/98. There is also more files included in the root directory of yours. In mines, only the following is available:

2AV.STR
DEMOXA.STR
MEDIEVIL.EXE
MEDRES.MWD
OVERLAYS Folder [Mines has the CREDITS.BIN]
SPEECH.STR

I also had cracked the correct button cheats for both games. Here they are, and I hope they work for you:

[b]Medievil[/b]

Cheat Mode: 
Pause game play, then hold L2 and press Triangle, Circle(2), Triangle, Square, Circle, Left, Circle, Up, Down.

Extended Cheat Mode:
Pause game play, then hold L2 and press Square, Triangle, Circle, Up, Triangle(2), Right, Circle, Left(2), Square, Triangle, Right, Circle, Left(2), Square, Triangle, Circle, Down, Circle(2), Right.

[b]Medievil II[/b]

Cheat Mode: 
Pause game play, then hold L2 and press Down, Right, Circle, Left(2), Triangle, Right, Circle, Left(2).