Modpack version
0.5.4

Issue
The Weakness effect from EverlastingAbilities mod causes melee type mobs from damaging you after one hit from them. Skeletons are fine, but only from mobs that deal melee damage.
It seems pretty god mode from this point, so i removed it from myself.

Logs
Input pastebin link to crash-report or latest log, if applicable

Thank you for the report, I will investigate the issue.

Huh. The same applies for vanilla weakness potions, this isn't a mod issue :s
CyclopsMC/EverlastingAbilities#120

Fixed in 1.16 ;)

I disabled the Weakness Everlasting Ability to "remedy" this issue.