I'm having an issue with your mod, minecraft crashes whilst loading with this error java.lang.NoClassDefFoundError: techreborn/items/tools/ItemAdvancedDrill, now it may be something completly stupid on my end but can you guys tell me just what the problem here is the crash log any help would be appreciated. BTW i already have the latest versions of Forge for 1.12.2, Tech Reborn & Reborn Core so that's not the issue.

Cannot reproduce. Must be some mod interaction.

Could it be an outdated ic2 version without the drill api?

Could be. Support for them was only added in build 117 and @AnimalLover567 seems to be using build 108

I just updated to the latest beta of ic2 that issue is fixed.