Doom2 Demo question

I've been trying to do a series of chain demos in doom 2 but am meeting with little success. Essentially the idea is to play one level, save the game, then keep trying to do the next level and so on. However doom does odd things to my demo when I play it back, namely the fact that %99 of the monsters just aren't there, as if it were easiest mode and not ultra violence.

I use to be recording these in Doomsday but now wish to do it the 'old' way. Hope there's a way to do this.

A demo with saves is known as a TAS demo (tools-assisted speedrun), and to record one you need to use a specially modified version of the Doom engine, as this feature is not supported by the original game and most standard ports.

Two old TAS ports are tasdoom and tasmbf. Both are DOS-based, and not overly simple to use. Demos recorded with them will not play back with Doom2.exe (though tasdoom demos can often be converted - I'm not sure what the failure rate is). tasmbf demos play back with mbf and compatible ports (e.g. Eternity and Prboom).

The newest TAS port is Andrey Budko's modified Prboom, and this is quite simple to use. Like standard Prboom, it can be made to record a demo that will play back with Doom2.exe (just put "-complevel 0" in the command line). It comes with brief instructions, and there has been some discussion about how to use it in this forum. If you hit problems, ask, and I (or others) will try to help.

Sounds exactly like what I'm looking for, thank you very much.