I'm unsure on what end this needs fixing, but to me it looks like some incompat problem:

java.lang.IllegalArgumentException: Cannot get property PropertyEnum{name=half, clazz=class net.minecraft.block.BlockSlab$EnumBlockHalf, values=[top, bottom]} as it does not exist in BlockStateContainer{block=quark:stone_basalt_bricks_slab_double, properties=[prop]}
at net.minecraft.block.state.BlockStateContainer$StateImplementation.func_177229_b(BlockStateContainer.java:196)
at drzhark.customspawner.CustomSpawner.canCreatureSpawn(CustomSpawner.java:606)
at drzhark.customspawner.CustomSpawner.canCreatureTypeSpawnAtLocation(CustomSpawner.java:590)
at drzhark.customspawner.CustomSpawner.doCustomSpawning(CustomSpawner.java:309)
at drzhark.customspawner.handlers.SpawnTickHandler.worldTick(SpawnTickHandler.java:27)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_849_SpawnTickHandler_worldTick_WorldTickEvent.invoke(.dynamic)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:185)
at net.minecraftforge.fml.common.FMLCommonHandler.onPreWorldTick(FMLCommonHandler.java:282)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:694)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:613)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:149)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:471)
at java.lang.Thread.run(Thread.java:745)

I don't know why you would think that the mod compatibility issue is with mo' creatures, but this is actually a copy of #200. You can read the response there.