Hello! I've been having a bit of a crashing issue when I attempt to even launch the game. After removing all of my mods except for FEI, JEI, and Excore, the game launches just fine. I have a crash report on this Google Doc here. If you could perhaps take a look at that, and help me identify which mod I've got installed is the problem, I would greatly appreciate it, and if you need anything else I'll do my best to provide.

Latest version of FEI, the latest 1.8.9 version of JEI (which I believe is 2.28.18.186), Excore 1.5.3

Uhhm, you didn't open crash file to public access.
And it would be better, if you could post it on patebin or gist.

Oh! Oh, gosh, I'm so sorry! I have a new, working Pastebin link here. Very sorry.

No, not a big deal.
Looking at this crash, it actually is weird and caused by a mod.

Ok, in your opinion, which of mods that you have have somethign to do with spawners (really anything, from texture changing to complete overhaul)?

It's crash with Improving Minecraft, you can report it on his issue tracker. While it's not fixed, i'll keep this issue open.

Oh, ok, thank you! I don't really need the mod, as I added it as an afterthought, so I can just remove it. Thank you very much. I'll go ahead and report it on his issue tracker so that it might help him with conflicting mods.

Thanks for reporting it to him!
As issue is on his side, i'll consider this issue on my side fixed.