Reason why the game is stuck:

The Video BIOS ROM (located at c000:0000) is supposed to start with EE AA followed by one byte that stores the size of the ROM (in 512 bytes-blocks). This third byte is [es]:0002 in above case.

So what the game does: It tries to find out how big the ROM (and therefor the shadowed RAM area) is so it can use the RAM area right behind.

However, DOSBOX only writes EE AA but does not specifies the size. This breaks that part of the game.

The attached diff will change the Video BIOS such it specifies 32KB as size (the default). After applying that patch, the game will no longer be stuck.

Here's a way to run the game properly: As soon as the level starts, enter debug mode, then enter the command

SM 9a:62c8 50

After you have done that, you can jump, attack etc. without crashes.

I am not sure why the game changes the code in the first place. It seems like Prehistorik 2 believes that we are running a debugger (it messes around with int3) and wants to punish us for that..

Excellent work Fizzban, you also raise a valid point -
most forms of sophisticated game protection will
mess with INT1/3; the fact that dosbox responds
as a debugger to these may trigger alternative
codepaths designed to thwart reverse engineering.

heavydebug routines shouldn't be detectable as dosbox doesn't need to insert int 3 then