I just had a weird giant "hungry spider" spawn and pretty much ruin my game - he spawned randomly on level 2 of a dungeon and is stuck in the ceiling because he is so huge and every time he hits me he takes an item - from hotbar/inventory/or armor. He has all my tools now, and my bag of holding, and my armor, baubles, everything. I'm not sure how to kill it since every time he hits me he takes an item - even if I cheat in swords and armor they are gone in 5 seconds of fighting him. I was trying to kill him because I figured maybe he would drop the gear - but not sure how to even do it considering he is in the ceiling and hard to hit and if I can hit him he hits back and takes my sword(s) and armor. Also not sure where the gear would drop - probably in solid rock somewhere considering he is 95% in the ceiling.
Edit: Actually I guess there are two of them. Think it is too late for me to salvage the game - might start over with heavily edited SpecialMobs.cfg but the default config (everything on) is pretty much unplayable because its only a matter of time until you run into a totally broken mob.
It's not stuck in the ceiling, the model just starts at the floor. The hitbox is actually the spider's normal size, even. You basically have no chance of hitting it in melee without waila being on to tell you when you're looking at it, and good luck figuring out where it's actually standing so you can hit it with a bow.
They DO drop all your stuff when killed. Go into creative mode with some sort of weapon and kill them. Also, disable hungry spiders. Botania and Specialmobs have an interaction where hungry spiders shed string randomly, and then eat it immediately to grow larger, and larger... Specialmobs did not until recently have any limit on how big a hungry spider can get, thus you have... this problem. Compounding on the issue is that once a spider eats an item, it does not despawn. I'm not sure if the other Hungry mob types can get huge (probably not), but I disabled them too just in case.
Right now I'm having an issue where the Twilight Forest dimension is incredibly slow. I'm gonna run OPIS to find out why.
Edit: I have no idea why. Whatever's lagging the crap out of TF, opis can't see it. I used killall on a bunch of animals that were reportedly causing the most lag, and the TPS went DOWN. I'm guessing there's some sort of event handler that is just crapping out and reporting NaN to opis while sucking up all the cycles.
Edit2: To add to my confusion, it seems if I go to creative mode and just fly a little bit the lag goes away. I was starting to remove mods to see if one of them was the problem but nope, it's probably just minecraft's mob pathing glitching out, I think? TF still has chunk generation lag but that's normal for TF.