https://pastebin.com/dRJu24h9 So, I updated to 1.3, tried to see how my friend's modpack worked, and I found out that the "how" is that it doesn't. I can create a character, but when I try to actually load up, I get this error: I'm no developer, but I see the "particleRegionPadding" in the log, and I'd assume the issue is somewhere around there?
So, according to the steam version of this thread, the culprit was Tinted torches. and removing that mod worked for me.