Collaborative Recipe Droplist.

Which, if any, 2x buffs stack? 2x drop card, 1.2x family drop, the 2x buff from the winter thing. Do all 3 stack together, or none at all?

I'm pretty sure all 3 of those stack. If it doesn't cancel another it'll stack. For example, the clover buff from the springtime event canceled the winter one.

-2x card stacks with everything
-2x winter does not stack with other useable effects
-1.2x family stacks with everything unless event is active

For best results:
-2x drop event
-2x drop card
-2x drop winter buff