Whenever I spawn a Ferrouslime through it's spawn egg, it crashes the game. I am using Essential to play Alex's Caves so that might be an issue.

crash log?

I did some testing and realized that there is more to it. Apparently, whenever you kill a ferrouslime, it causes the game to freeze. Yet you can still save and exit from the world, but you cannot go back into the world afterwards. So it doesn't actually cause the game to crash but it still softlocks worlds.

crash log?