hello, just tried out this mod, and found out it causes the game to crash before the game window loads

there was no crash report generated so heres my latest log:
https://pastebin.com/g7RUg687

You have the wrong Mixin version loaded. Try using Mixin 0.7-0.8 Compat

Thanks for the bug report and pointer. I don't know if there is much I can do to fix this. 1.12 Mixin seems to be less comptabile and updating the mixin version my mod uses caused other modpacks to crash.

Actually, that is not Fiona the Mortal's fault, it is
the forge team's fault for not embedding it.

using that mixin mod linked solved the problem, thanks.

You can blame the forge team.