Hardoom

I made this wad. Why?

All enemy health and missile damage are effectively doubled, but your weapons do less damage, give less ammo, and use up more ammo! The pickups give half as many as they usually would, and both the maximum health and armour values are both capped at 100%.

Play any wad with it, and prepare to die more times to a zombieman than you would like to.

Hardoom.zip

Oh, and there is an opposite. 

All enemy health and missile damage are effectively halved, but your weapons do more damage, give more ammo, and use up less ammo! The pickups give twice as many as they usually would, and both the maximum health and armour values are both capped at 400%!

Play any wad with it, and prepare to kill more Cyberdemons than you can handle!

EZDoom.zip

Well, it certainly does what you said it does. Here's a video where I barely manage to survive E1M1 on UV after a few tries:

And here's a video where I try HNTR:

There is a serious technical issue: weapon switching is completely broken. I could only manually switch to weapons 1 (melee) and 2 (pistol). For anything else, I had to rely on autoswitch. In the HNTR video, there's one point where I deliberately try to trigger autoswitch by running out of bullets. EZDoom has the same problem.

Aside from that, I don't like it. It drastically alters the original balance of the game to its detriment. I imagine the playstyle that is necessary to survive UV in this mod would be slow and tedious, and even Nightmare mode is more fun and fair.