https://paste.dimdev.org/edekaqimug.mccrash just a few fish according to vanilla tweaks
https://paste.dimdev.org/ijasokemon.mccrash hammer core according to vanilla tweaks

No, line 9 in both are the same: at com.oitsjustjose.vtweaks.event.mobtweaks.ChallengerMobs.registerEvent(ChallengerMobs.java:40)
I was looking and it seems that you have set Challenger Mobs Rarity to 0 instead of just disabling them? I can make a catch for this but a good "right now" solution is to turn Enable Tweak to false and setting Rarity to anything larger than 0.

thanks