The original Better Hurt Timer can be found here, go try it if you aren't sure which one to use, or just read the page if are confused on the functionality of this mod, that page explains it better. It even has

This mod will likely stay on 1.12.2 for now.

This is a fork of Awekyuwusu's Better Hurt Timer (specifically its 1.5.0.1 version), a mod which reworks immunity frames to be damage source-specific as well as increasing dependency on Attack Speed in tandem. It also depends on Mixinbooter now.

Like the original (which you should still try out if you have the time, it's very well made), damage sources can be configured to have a specific amount of immunity frames, or alternatively be forced to accumulate (stack) if multiple instances of damage occur, with the final damage amount being dealt at the end of said frames. The stacking in specific was one of the major reasons this fork was made, as it was removed in later versions. That and Mixinsanity.

Armor and shields are only damaged every 1/4 of a second to prevent breakage, and hurt animations cannot interrupt each other. You can also prevent certain sources from applying knockback!

The mod also ports 1.16+ knockback scaling to 1.12.2.

With that being said, going back several versions of a mod may be prone to issues. I will attempt to fix these as I find them, but if the original BHT works fine for you already, you might not even need this mod. That mod may not be receiving support anymore, though. Don't bug the dev.

List of mods with ""explicit"" compatibility:

End Expansion, that mod's entities should properly integrate with Damage Stacking now.
EnderSkills, although this is moreso due to being a fork of 1.5.0.1.

Known issues:

Potion Core, disable the custom projectile I-Frames, otherwise they will interfere with this mod's behavior.

Feel free to suggest any changes, as long as they are within reason.

If you're a nerd, there's also a PreLivingAttackEvent and PreLivingKnockbackEvent, but I'm not sure why you'd use those.

Again, massive kudos to Awekyuwusu and the other kind folks who contributed to BHT; this fork didn't change much of their work.

Oh, and if you're using PhanagledHurtTimer, just stick to that (not that it exists or anything)

Worse Hurt Timer