ClassCastException: class net.minecraft.world.damagesource.DamageSource cannot be cast to class net.puffish.skillsmod.access.DamageSourceAccess

This is the root cause. It happens when a LivingEntity takes damage and Pufferfish Skills attempts to inject into the damage process using a Mixin. The cast to DamageSourceAccess fails because the DamageSource object is not of the expected modified class, likely due to a conflict or bad state after updates or removals.

This is a Mixin injection conflict, and the exception is fatal:

at net.minecraft.world.entity.LivingEntity.handler$puffish_skills$injectAtApplyDamage(...)
Had to remove pufferfish to get it working, happens when entities spawn in

-tried removing all PF mod files
-This happened during the client tick
-The issue is with Puffish Skills trying to cast a vanilla DamageSource into a mod-specific interface (DamageSourceAccess)
-There's no proper instanceof check, so the cast fails and crashes the game

puffish_skills-0.16.3-1.21-neoforge.jar

Thanks for reporting. However I can't reproduce the issue. I have tested on NeoForge 21.1.57 and just Skills 0.16.3 mod. If possible please send a crash report.

crash-2025-06-24_12.08.57-server.txt

I have also tested on the same NeoForge that you use, and I still can't reproduce the issue. You have a lot of mods, so it is very likely caused by a conflict with another mod. Please try with other mods disabled.