Preface: I have vaniallafix installed

When using the shadowium blade and wearing botania or extra botany armour, then the game crashes to the point where you cannot re-enter your world (vanilla fix blocks his telling you of the crash on each re-entry attempt but I believe its because it fully corrupts the world) to the point where you need to restore from a backup. The error is

java.lang.NoSuchMethodError: vazkii.botania.api.mana.IManaDiscountArmor.getDiscount(

You can get a similar error from botania itself so there is an issue on that end but those only cause minor errors and not corruption so here's the full Pastebin https://paste.dimdev.org/ihadamivib.mccrash

weird. I asked some people to do that but none of them got a crash. need further investigation

Huh, since you were not able to reproduce it, I'll give a bit more detail, The only other thing I think could be related is that I was testing this against the Gaia guardian 3. (In hindsight I don't think i tested against any other mobs)
The crash happened when I hit the boss with the Shaowium katana.
And just to add, although I'm fairly sure these do not affect it, I know it crashed with both Terrasteel and maid armour.
And on the off chance, it is another mod causing issues this was tested on the pack: The Culmination version 2.2.0. (I would suggest taking ToMeTinkers out because it causes the load time to be quadrupled to over 20 minutes)

the crash is caused because some mod is using outdated botania api