A detailed walkthrough of the error, its code path and all known details is as follows:

-- Head --
Thread: Render thread
Stacktrace:
at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.8.0_281] {}
at java.util.ArrayList$Itr.next(Unknown Source) ~[?:1.8.0_281] {}
at net.minecraft.client.renderer.entity.LivingRenderer.func_225623_a_(LivingRenderer.java:202) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default,pl:mixin:APP:obfuscate.mixins.json:client.OptifineLivingRendererMixin,pl:mixin:APP:charm.mixins.json:accessor.LivingRendererAccessor,pl:mixin:A}
at net.minecraft.client.renderer.entity.MobRenderer.func_225623_a_(MobRenderer.java:47) ~[?:?] {re:classloading,xf:OptiFine:default,re:mixin}
at net.minecraft.client.renderer.entity.MobRenderer.func_225623_a_(MobRenderer.java:20) ~[?:?] {re:classloading,xf:OptiFine:default,re:mixin}
-- Entity being rendered --
Details:
Entity Type: alexsmobs:kangaroo (com.github.alexthe666.alexsmobs.entity.EntityKangaroo)
Entity ID: 4316
Entity Name: 袋鼠
Entity's Exact location: -529.82, 66.00, -542.74
Entity's Block location: World: (-530,66,-543), Chunk: (at 14,4,1 in -34,-34; contains blocks -544,0,-544 to -529,255,-529), Region: (-2,-2; contains chunks -64,-64 to -33,-33, blocks -1024,0,-1024 to -513,255,-513)
Entity's Momentum: 0.00, -0.00, 0.00
Entity's Passengers: [EntityKangaroo['袋鼠'/4319, l='ClientLevel', x=-529.82, y=66.66, z=-542.74]]
Entity's Vehicle: ERROR NullPointerException: null

-- Renderer details --
Details:
Assigned renderer: com.github.alexthe666.alexsmobs.client.render.RenderKangaroo@212cb193
Location: -76.13,-37.16,4.96 - World: (-77,-38,4), Chunk: (at 3,-3,4 in -5,0; contains blocks -80,0,0 to -65,255,15), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Rotation: -45.0
Delta: 0.49995613
Stacktrace:
at net.minecraft.client.renderer.entity.EntityRendererManager.func_229084_a_(EntityRendererManager.java:311) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default,pl:mixin:APP:byg.mixins.json:client.MixinEntityRendererManager,pl:mixin:A}
at net.minecraft.client.renderer.WorldRenderer.func_228418_a_(WorldRenderer.java:2120) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default,xf:fml:better_diving:WorldRenderer Transformer,xf:fml:sereneseasons:temperature_transformer,pl:mixin:APP:blue_skies.mixins.json:WorldRendererMixin,pl:mixin:APP:citadel.mixins.json:client.WorldRendererMixin,pl:mixin:APP:supplementaries.mixins.json:ParrotPartyMixin,pl:mixin:APP:betterendforge.mixins.json:WorldRendererMixin,pl:mixin:APP:structure_gel.mixins.json:WorldRendererMixin,pl:mixin:APP:tenshilib.mixins.json:WorldRenderAccessor,pl:mixin:APP:lightoverlay-forge.mixins.json:MixinLevelRenderer,pl:mixin:APP:charm.mixins.json:WorldRendererMixin,pl:mixin:APP:cgm.mixins.json:client.WorldRendererMixin,pl:mixin:APP:sereneseasons.mixins.json:client.MixinWorldRenderer,pl:mixin:APP:immersiveengineering.mixins.json:accessors.client.WorldRendererAccess,pl:mixin:APP:immersiveengineering.mixins.json:coremods.client.WorldRendererMixin,pl:mixin:APP:flywheel.mixins.json:CancelEntityRenderMixin,pl:mixin:APP:flywheel.mixins.json:FixFabulousDepthMixin,pl:mixin:APP:flywheel.mixins.json:RenderHooksMixin,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorWorldRenderer,pl:mixin:APP:assets/botania/botania.mixins.json:MixinWorldRenderer,pl:mixin:A}
at net.minecraft.client.renderer.WorldRenderer.func_228426_a_(WorldRenderer.java:1742) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default,xf:fml:better_diving:WorldRenderer Transformer,xf:fml:sereneseasons:temperature_transformer,pl:mixin:APP:blue_skies.mixins.json:WorldRendererMixin,pl:mixin:APP:citadel.mixins.json:client.WorldRendererMixin,pl:mixin:APP:supplementaries.mixins.json:ParrotPartyMixin,pl:mixin:APP:betterendforge.mixins.json:WorldRendererMixin,pl:mixin:APP:structure_gel.mixins.json:WorldRendererMixin,pl:mixin:APP:tenshilib.mixins.json:WorldRenderAccessor,pl:mixin:APP:lightoverlay-forge.mixins.json:MixinLevelRenderer,pl:mixin:APP:charm.mixins.json:WorldRendererMixin,pl:mixin:APP:cgm.mixins.json:client.WorldRendererMixin,pl:mixin:APP:sereneseasons.mixins.json:client.MixinWorldRenderer,pl:mixin:APP:immersiveengineering.mixins.json:accessors.client.WorldRendererAccess,pl:mixin:APP:immersiveengineering.mixins.json:coremods.client.WorldRendererMixin,pl:mixin:APP:flywheel.mixins.json:CancelEntityRenderMixin,pl:mixin:APP:flywheel.mixins.json:FixFabulousDepthMixin,pl:mixin:APP:flywheel.mixins.json:RenderHooksMixin,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorWorldRenderer,pl:mixin:APP:assets/botania/botania.mixins.json:MixinWorldRenderer,pl:mixin:A}
at net.minecraft.client.renderer.GameRenderer.func_228378_a_(GameRenderer.java:1022) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,xf:OptiFine:default,xf:fml:better_diving:GameRenderer Transformer,pl:mixin:APP:cgm.mixins.json:client.GameRendererMixin,pl:mixin:APP:flywheel.mixins.json:StoreProjectionMatrixMixin,pl:mixin:APP:mixins.modernui-forge.json:AccessGameRenderer,pl:mixin:A}

-- Affected level --
Details:
All players: 1 total; [ClientPlayerEntity[''/731, l='ClientLevel', x=-453.70, y=101.54, z=-547.70]]
Chunk stats: Client Chunk Cache: 4761, 2771
Level dimension: minecraft:overworld
Level spawn location: World: (-128,63,16), Chunk: (at 0,3,0 in -8,1; contains blocks -128,0,16 to -113,255,31), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 7063 game time, 7063 day time
Server brand: forge
Server type: Integrated singleplayer server
Stacktrace:
at net.minecraft.client.world.ClientWorld.func_72914_a(ClientWorld.java:617) ~[?:?] {re:mixin,re:classloading,xf:OptiFine:default,xf:fml:xaeroworldmap:xaero_wm_clientworldclass,xf:fml:xaerominimap:xaero_clientworldclass,pl:mixin:APP:blue_skies.mixins.json:ClientWorldMixin,pl:mixin:APP:architectury.mixins.json:MixinClientLevel,pl:mixin:APP:abnormals_core.mixins.json:client.ClientWorldMixin,pl:mixin:APP:mixins.sndctrl.json:MixinClientWorld,pl:mixin:APP:endergetic.mixins.json:ClientWorldMixin,pl:mixin:APP:create.mixins.json:BreakProgressMixin,pl:mixin:A}
at net.minecraft.client.Minecraft.func_71396_d(Minecraft.java:2029) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:623) ~[?:?] {re:mixin,pl:accesstransformer:B,pl:runtimedistcleaner:A,re:classloading,pl:accesstransformer:B,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.client.main.Main.main(Main.java:184) ~[1.16.5.jar:?] {re:classloading,pl:runtimedistcleaner:A}
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_281] {}
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_281] {}
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_281] {}
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_281] {}
at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:51) ~[forge-1.16.5-36.2.0.jar:36.2] {}
at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-8.0.9.jar:?] {}
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-8.0.9.jar:?] {}
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-8.0.9.jar:?] {}
at cpw.mods.modlauncher.Launcher.run(Launcher.java:82) [modlauncher-8.0.9.jar:?] {re:classloading}
at cpw.mods.modlauncher.Launcher.main(Launcher.java:66) [modlauncher-8.0.9.jar:?] {re:classloading}