When loading into a world the entities will not become infernal (i think) because their target is null. Not sure what this means, but here is what happens in the crash log. This only happens when Infernal mobs is loaded together with other mods in my modpack TwiCraft, but only for 1.20.1 versions. the 1.19.2 version works fine

Description: Ticking entity

java.lang.NullPointerException: Cannot invoke "net.minecraft.world.entity.Entity.m_269291_()" because "attacker" is null
at atomicstryker.infernalmobs.common.EntityEventHandler.onEntityLivingHurt(EntityEventHandler.java:100) ~[infernalmobs-1.20.1.0.jar%23297!/:1.20.1.0] {re:classloading}
at atomicstryker.infernalmobs.common.EntityEventHandler_onEntityLivingHurt_LivingHurtEvent.invoke(.dynamic) ~[infernalmobs-1.20.1.0.jar%23297!/:1.20.1.0] {re:classloading,pl:eventbus:B}
at net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:73) ~[eventbus-6.0.5.jar%2387!/:?] {}
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:315) ~[eventbus-6.0.5.jar%2387!/:?] {}
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:296) ~[eventbus-6.0.5.jar%2387!/:?] {}
at net.minecraftforge.common.ForgeHooks.onLivingHurt(ForgeHooks.java:292) ~[forge-1.20.1-47.2.1-universal.jar%23357!/:?] {re:classloading}
at net.minecraft.world.entity.LivingEntity.m_6475(LivingEntity.java:1617) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_6469(LivingEntity.java:1112) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_142535_(LivingEntity.java:1521) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.level.block.Block.m_142072_(Block.java:379) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:architectury-common.mixins.json:inject.MixinBlock,pl:mixin:APP:cfm.mixins.json:client.BlockMixin,pl:mixin:APP:puzzleslib.common.mixins.json:accessor.BlockAccessor,pl:mixin:APP:structure_gel.mixins.json:BlockMixin,pl:mixin:A}
at net.minecraft.world.entity.Entity.m_7840_(Entity.java:1128) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorEntity,pl:mixin:APP:balm.mixins.json:EntityMixin,pl:mixin:APP:supplementaries-common.mixins.json:EntityMixin,pl:mixin:APP:curios.mixins.json:AccessorEntity,pl:mixin:APP:tombstone.mixins.json:EntityMixin,pl:mixin:APP:blueprint.mixins.json:EntityMixin,pl:mixin:APP:structure_gel.mixins.json:EntityMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_7840_(LivingEntity.java:312) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.Entity.m_6478_(Entity.java:661) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorEntity,pl:mixin:APP:balm.mixins.json:EntityMixin,pl:mixin:APP:supplementaries-common.mixins.json:EntityMixin,pl:mixin:APP:curios.mixins.json:AccessorEntity,pl:mixin:APP:tombstone.mixins.json:EntityMixin,pl:mixin:APP:blueprint.mixins.json:EntityMixin,pl:mixin:APP:structure_gel.mixins.json:EntityMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_21074_(LivingEntity.java:2195) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_7023_(LivingEntity.java:2132) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_8107_(LivingEntity.java:2605) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.Mob.m_8107_(Mob.java:536) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorMob,pl:mixin:APP:immersive_armors.mixins.json:MobEntityMixin,pl:mixin:APP:tombstone.mixins.json:MobMixin,pl:mixin:APP:moonlight-common.mixins.json:EntityMixin,pl:mixin:A}
at net.minecraft.world.entity.monster.Monster.m_8107_(Monster.java:42) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,re:computing_frames,re:classloading,pl:mixin:APP:tombstone.mixins.json:MonsterMixin,pl:mixin:A}
at net.minecraft.world.entity.monster.AbstractSkeleton.m_8107_(AbstractSkeleton.java:116) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:supplementaries-common.mixins.json:AbstractSkeletonMixin,pl:mixin:A}
at net.minecraft.world.entity.LivingEntity.m_8119_(LivingEntity.java:2298) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorLivingEntity,pl:mixin:APP:bookshelf.common.mixins.json:patches.entity.MixinLivingEntity,pl:mixin:APP:immersive_armors.mixins.json:MixinLivingEntity,pl:mixin:APP:supplementaries-common.mixins.json:LivingEntityMixin,pl:mixin:APP:curios.mixins.json:MixinLivingEntity,pl:mixin:APP:tombstone.mixins.json:LivingEntityMixin,pl:mixin:APP:caelus.mixins.json:MixinLivingEntity,pl:mixin:APP:betterdeserttemples.mixins.json:PharaohKilledMixin,pl:mixin:APP:ecologics-common.mixins.json:LivingEntityMixin,pl:mixin:A}
at net.minecraft.world.entity.Mob.m_8119_(Mob.java:337) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:bookshelf.common.mixins.json:accessors.entity.AccessorMob,pl:mixin:APP:immersive_armors.mixins.json:MobEntityMixin,pl:mixin:APP:tombstone.mixins.json:MobMixin,pl:mixin:APP:moonlight-common.mixins.json:EntityMixin,pl:mixin:A}
at net.minecraft.world.entity.monster.Skeleton.m_8119_(Skeleton.java:73) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:supplementaries-common.mixins.json:SkeletonMixin,pl:mixin:A}
at net.minecraft.server.level.ServerLevel.m_8647_(ServerLevel.java:693) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:cupboard.mixins.json:ServerAddEntityMixin,pl:mixin:APP:citadel.mixins.json:ServerLevelMixin,pl:mixin:APP:supplementaries-common.mixins.json:ServerLevelMixin,pl:mixin:APP:betterdeserttemples.mixins.json:ServerLevelMixin,pl:mixin:APP:blueprint.mixins.json:ServerLevelMixin,pl:mixin:APP:crafttweaker.mixins.json:common.transform.world.level.MixinServerLevel,pl:mixin:A}
at net.minecraft.world.level.Level.m_46653_(Level.java:479) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:twilightforest:cloud,re:classloading,pl:accesstransformer:B,xf:fml:twilightforest:cloud,pl:mixin:APP:citadel.mixins.json:LevelMixin,pl:mixin:A}
at net.minecraft.server.level.ServerLevel.m_184063_(ServerLevel.java:343) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:cupboard.mixins.json:ServerAddEntityMixin,pl:mixin:APP:citadel.mixins.json:ServerLevelMixin,pl:mixin:APP:supplementaries-common.mixins.json:ServerLevelMixin,pl:mixin:APP:betterdeserttemples.mixins.json:ServerLevelMixin,pl:mixin:APP:blueprint.mixins.json:ServerLevelMixin,pl:mixin:APP:crafttweaker.mixins.json:common.transform.world.level.MixinServerLevel,pl:mixin:A}
at net.minecraft.world.level.entity.EntityTickList.m_156910_(EntityTickList.java:54) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:classloading}
at net.minecraft.server.level.ServerLevel.m_8793_(ServerLevel.java:323) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:cupboard.mixins.json:ServerAddEntityMixin,pl:mixin:APP:citadel.mixins.json:ServerLevelMixin,pl:mixin:APP:supplementaries-common.mixins.json:ServerLevelMixin,pl:mixin:APP:betterdeserttemples.mixins.json:ServerLevelMixin,pl:mixin:APP:blueprint.mixins.json:ServerLevelMixin,pl:mixin:APP:crafttweaker.mixins.json:common.transform.world.level.MixinServerLevel,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_5703_(MinecraftServer.java:893) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_5705_(MinecraftServer.java:814) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:A}
at net.minecraft.client.server.IntegratedServer.m_5705_(IntegratedServer.java:89) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:runtimedistcleaner:A,re:classloading,pl:mixin:APP:blueprint.mixins.json:client.IntegratedServerMixin,pl:mixin:APP:smoothboot.mixins.json:client.IntegratedServerMixin,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.m_130011_(MinecraftServer.java:661) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_206580_(MinecraftServer.java:251) ~[client-1.20.1-20230612.114412-srg.jar%23352!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:A}
at java.lang.Thread.run(Thread.java:833) ~[?:?] {re:mixin}

Thanks for reporting this. I have made a bugfix for 1.20.1 and 1.20.2 and pushed new builds to curse
9646c6b
e451811

No worries, let me know if you need the full debug file with all the info. this was just the description of what happened.

If you could verify that the change fixes the issue? That would be good.

Installed the new one, and everything works now. Thanks allot. now the new release for 1.20.1 for my modpack is coming to a close. Only missing 1 mod update to release it

Good to hear!