Life Force is a mod I made for Doom a few years back. It was designed as a ‘mutator’ — a mod that adds no graphic/sound assets, just scripting and configuration code to remix the standard Doom 2 assets to make something new. I later added in versions for Heretic and Hexen as well.
This is a magic-themed weapons mod that combines health and ammo into a single substance: Life Force. Weapons are replaced with attacks that drain health, but monsters also release health to compensate.
It’s designed to run on fairly recent versions of GZDoom, though it might work on other ZDoom forks as well.