not a woman
I have a couple "new" monsters in some upcoming levels. I'm only using DeHacked, though. Several source ports have the option to create new monsters from scratch, but I try to make it so my levels will work in whatever port. I used DeHacked to make some new enemies. For example, making spectres of monsters is a good place to start. Spectre imps are good.
I played a good wad that made a completely invisible monster that is unable to be killed, made no sound and attacks rather quickly, then put it behind a fake wall so that it acts like the fireball launcher from Rise of the Triad.
Stronger Barons are good. Copy and paste a Baron's information to something like Dead Lost Soul or Commander Keen and then change the color bits so that the green in him appears red (this will change his hands as well as blood, but not his projectile unfortunately). You can also make him faster and with more HP. The disadvantage is that he WILL fight with normal Barons or Hell Knights. But they make good Mid-bosses if you speed them up.
You can also copy and paste the Cyberdemon to something and decrease his HP to make a Cyberdemon mid-boss. These will also fight with normal Cyberdemons.
One thing I did do for an upcoming level is replace the Nazis with Player graphics, so that you have a Nazi that looks like the Doom Marine. He still attacks the same way, though. I changed his speed so he's very fast, cranked up the HP, changed the color to red, and changed the sounds of course. You now have an evil marine like a zombie, but still in his outfit! The way the nazis attack tends to be painful when they have 200+ health and can move as fast as an Arch-Vile.
There will be a sort of "new" monster in Dream.wad when it's released. You should know it when you approach the room, so look for it.
The other day I made a new "boss" with DeHacked and some graphics replacing. I made the Cacodemon have 16,000 HP and move a lot faster with a lower pain chance and faster reaction time, then changed the frames for several monster attacks to make it attack like a sped-up Mancubs, then a Revenant. So you have seven fireballs coming at you, one of which heat-seeks. To make him more difficult, I made his pain sequence include a Pain Elemental's Lost Soul spawn, and then just to make him impossible to punch, I replaced his close range attack with a very sped-up Cyberdemon, so you're hit with three rockets at once. Then I went through and replaced all the frames I needed to with the Fire Imp from Hexen or Heretic, I forget which one. It was interesting, but got rid of about five monsters total.
ZooM, the ZDoom Racing Mod