multimob-1.0.4a
primitivemobs-1.2.3a

---- Minecraft Crash Report ----
// Uh... Did I do that?

Time: 2019-01-26 13:45:49 EST
Description: Ticking entity

java.lang.ClassCastException: java.lang.Byte cannot be cast to java.lang.Integer
at net.daveyx0.primitivemobs.entity.monster.EntityBabySpider.getGrowthLevel(EntityBabySpider.java:196)
at net.daveyx0.primitivemobs.entity.monster.EntityBabySpider.canBeSteered(EntityBabySpider.java:84)
at net.minecraft.entity.EntityLiving.canPassengerSteer(EntityLiving.java:1601)
at net.minecraft.entity.EntityLivingBase.travel(EntityLivingBase.java:1839)
at net.daveyx0.primitivemobs.entity.monster.EntityBabySpider.travel(EntityBabySpider.java:376)
at net.minecraft.entity.EntityLivingBase.onLivingUpdate(EntityLivingBase.java:2393)
at net.minecraft.entity.EntityLiving.onLivingUpdate(EntityLiving.java:678)
at net.minecraft.entity.monster.EntityMob.onLivingUpdate(EntityMob.java:45)
at net.minecraft.entity.EntityLivingBase.onUpdate(EntityLivingBase.java:2179)
at net.minecraft.entity.EntityLiving.onUpdate(EntityLiving.java:377)
at net.minecraft.entity.monster.EntityMob.onUpdate(EntityMob.java:50)
at net.daveyx0.primitivemobs.entity.monster.EntityPrimitiveSpider.onUpdate(EntityPrimitiveSpider.java:79)
at net.daveyx0.primitivemobs.entity.monster.EntityBabySpider.onUpdate(EntityBabySpider.java:153)
at net.minecraft.world.World.updateEntityWithOptionalForce(World.java:1993)
at net.minecraft.world.World.updateEntity(World.java:1955)
at net.minecraft.world.World.redirect$updateEntity$zbl000(World.java:5117)
at net.minecraft.world.World.updateEntities(World.java:1759)
at net.minecraft.client.Minecraft.runTick(Minecraft.java:1847)
at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1098)
at net.minecraft.client.Minecraft.run(Minecraft.java:3942)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at pl.skmedix.loader.GameLoader.main(GameLoader.java:35)

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

-- Entity being ticked --
Entity Type: primitivemobs:baby_spider (net.daveyx0.primitivemobs.entity.monster.EntityBabySpider)
Entity ID: 10608
Entity Name: Baby Spider
Entity's Exact location: 329.33, 18.00, 216.25
Entity's Block location: World: (329,18,216), Chunk: (at 9,1,8 in 20,13; contains blocks 320,0,208 to 335,255,223), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: 0.00, -0.08, 0.00
Entity's Passengers: []
Entity's Vehicle: ERROR NullPointerException: null
Entity NBT: ERROR ReportedException: Saving entity NBT

Also get this one

---- Minecraft Crash Report ----
// Don't be sad. I'll do better next time, I promise!

Time: 2019-01-26 14:41:17 EST
Description: Ticking entity

java.lang.ClassCastException: com.google.common.base.Present cannot be cast to java.lang.Integer
at net.daveyx0.primitivemobs.entity.passive.EntityGroveSprite.getSaplingTimer(EntityGroveSprite.java:525)
at net.daveyx0.primitivemobs.entity.passive.EntityGroveSprite.onUpdate(EntityGroveSprite.java:202)
at net.minecraft.world.World.updateEntityWithOptionalForce(World.java:1993)
at net.minecraft.world.World.updateEntity(World.java:1955)
at net.minecraft.world.World.redirect$updateEntity$zbl000(World.java:5117)
at net.minecraft.world.World.updateEntities(World.java:1759)
at net.minecraft.client.Minecraft.runTick(Minecraft.java:1847)
at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1098)
at net.minecraft.client.Minecraft.run(Minecraft.java:3942)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at pl.skmedix.loader.GameLoader.main(GameLoader.java:35)

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

-- Entity being ticked --
Entity Type: primitivemobs:grovesprite (net.daveyx0.primitivemobs.entity.passive.EntityGroveSprite)
Entity ID: 5625
Entity Name: Grove Sprite
Entity's Exact location: 139.50, 69.00, 249.50
Entity's Block location: World: (139,69,249), Chunk: (at 11,4,9 in 8,15; contains blocks 128,0,240 to 143,255,255), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: -0.04, -0.08, -0.04
Entity's Passengers: []
Entity's Vehicle: ERROR NullPointerException: null
Entity NBT: ERROR ReportedException: Saving entity NBT

Yeah this is pretty common, I had to disable them. I hope davey looks at it soon.