Versions

Betweenlands version:

v3.4.1

Forge version:

forge-14.23.5.2768

Singleplayer or Multiplayer:

Singleplayer

Installed mods:

FTB Revelation Modpack v2.0.6

Spectrite v1.6.7
DrZhark's Mo'Creatures 12.0.5
OptiFine_1.12.2_HD_U_E2

Link to full crash log

https://gist.github.com/sersimovi/28a9a159fc70cd04ae475bfb3e2e4e5b

Description of the problem

How to reproduce:

I installed the FTB Revelation modpack using Twitch and then added a couple mods. The game crashes displaying an error message that says 'It looks like you're using an unsupported modified version of the game.' and then this:

'The game crashed whilst there was a severe problem during mod loading that has caused the game to fail
The game crashed whilst there was a severe problem during mod loading that has caused the game to fail
Error: net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from The Betweenlands (thebetweenlands)'

If I delete the betweenlands mod the game runs fine. What's causing this?

(I tried having the same mods working without twitch and still the same error.)

Pictures:

https://imgur.com/XHbNRlt

Duplicate of #737.
This was already reported to Project Red and fixed on their side but not released yet.
More specifically it's the Project Red - Mechanical mod that's causing it.