My game is Crashing and i dont know why. I assume its alexs mod, because of the report :

java.lang.NoSuchFieldError: DIRT
at com.github.alexthe666.alexsmobs.entity.EntityFly.canFlySpawn(EntityFly.java:115) ~[alexsmobs-1.15.1.jar%2352!:1.15.1] {re:classloading}
at net.minecraft.world.entity.SpawnPlacements.m_21759_(SpawnPlacements.java:63) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.level.NaturalSpawner.m_46995_(NaturalSpawner.java:226) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading}
at net.minecraft.world.level.NaturalSpawner.m_47038_(NaturalSpawner.java:174) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading}
at net.minecraft.world.level.NaturalSpawner.m_47045_(NaturalSpawner.java:124) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading}
at net.minecraft.world.level.NaturalSpawner.m_47029_(NaturalSpawner.java:114) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading}
at net.minecraft.server.level.ServerChunkCache.m_8490_(ServerChunkCache.java:355) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.level.ServerChunkCache.m_142483_(ServerChunkCache.java:311) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.level.ServerLevel.m_8793_(ServerLevel.java:278) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.m_5703_(MinecraftServer.java:868) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.m_5705_(MinecraftServer.java:808) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.client.server.IntegratedServer.m_5705_(IntegratedServer.java:86) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.m_130011_(MinecraftServer.java:668) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.m_177918_(MinecraftServer.java:258) ~[client-1.18.1-20211210.034407-srg.jar%2366!:?] {re:classloading,pl:accesstransformer:B}
at java.lang.Thread.run(Thread.java:833) [?:?] {}

Yep I got the same issue

Same issue started a day ago

Same - everyone has mentioned to revert back to forge 39.0.17 because that's when forge removed their forge:DIRT reference which is what is causing this apparently. I'm curious why I only started noticing this issue a day ago as well though. I've been using this mod for quite some time with forge 39.0.19 and it wasn't an issue until recently.

Same

I've had the same issue with Alex's Mobs 1.15.1 file. But the 1.16.0 release seems to have fixed the issue. (only just updated it and it seems alright so far.)

same issue here