This mod completely disables HP regeneration for all enemies.
Leoetlino was the brains behind this operation, but is too humble to admit it.
This requires a switch running BOTW 1.6 (the latest update at time of writing).
You also need to have the DLC installed, but if you don't have that, why would you need the mod?
Place the patch file on your SD card at the location
Then boot your switch into CFW using your preferred method, and when you start BOTW the mod will be applied automatically- no need to start a new game.
To uninstall, remove the .ips file from your SD card.
I have only tested this on Atmosphere 10.3. If you're using an old version, or a different CFW entirely then I wish you luck but cannot assist you.
I would be stunned if this is somehow incompatible with any other mod, as the change is so small and specific. If Nintendo patches BOTW again however, it's almost certainly going to break until I can update.