Mod Conflict?
Log: https://mclo.gs/RDljjkz

That fixed it, thanks

Wasn't armorcurve or quark. Still trying to find out if there's a conflict. I don't know why it's crashing when I try to spawn the cave dweller with its spawn egg

Try using Forge 40.1.16 or later
It seems earlier versions didn't have the step height attribute / kept adding and removing it

In general it's recommended to use the latest / stable forge version due to various bug fixes