Compile the following template. Fields marked with (*) are mandatory, Fields with (-) are optional, Fields with (!) are mandatory in case of crash or bug

Type of Issue/Request (Bug / Crash / Suggestion / Translation / ...):

Crash

Version of the mod or build number:

"The 1.12 update! READ CHANGELOG!", as stated by curse.

Are you a Single Player, a Multiplayer Client (You are a player in a server) or Server Side?:

Singleplayer

Minecraft Version (1.9.4, 1.10, 1.10.2, 1.11.2...):

1.12

Description (or what were you doing when it crashed):

I tried to boot up MC and got this crash

https://pastebin.com/3G7m4EzQ

Pastebin of the log (fml-client-latest.log from your instance/logs folder):

ModPack (or list of mods via Pastebin. If using a modified modpack, write BOTH the modpack AND the link to the full mod list):

(!)

Pastebin of the config file (extraalchemy.cfg from your instance/config folder):

It didn't even generate.

OS and Java version (Java8 + Windows10 / Java7 + MacOS / ...):

(!)

Java 8, windows 10

Other information that you think might be useful:

(-)

Issue appears to be related to Tough as Nails, as well.

Yup, it's a known bug, it will be fixed in the next version (eta unknown, I'm recovering from an injury)