Creating the animations that I couldn't just yoink and twist from Mixamo.
The character's rig is from Mixamo's auto rigger and it's of course just a barebones forward kinematics rig, making animating extremely time consuming. So to save some time in animating I added inverse kinematics to the arms and legs.
I encountered some problems with pasting the flipped poses (only animating other hand then copy pasting a flipped pose tot the other side). Pasting flipped poses to the IK target bones worked well but any bones that had the Mixamo naming scheme didn't (literally nothing happened). I thought about making a driver for this (slider from open palm to closed fist) but I don't have enough animations to justify the time that would be spent on that, maybe later though (haven't done it before so it would take a little extra time).
All this, just means that the arm is easy to animate but when making a fist I have to pose every single finger bone (also I can copy it now that I've done it once), which isn't bad enough to start messing with the rig, possibly breaking it in the process. I'm pretty cautious with the rig because it breaks easily for the purpose of importing animations from Mixamo.
For baking the constrained (IK, copy rotation etc.) animations I used the same method that I've used before explained in this post.