Combine mixamo animations with own rig / animation possible? So I downloaded a bunch of mixamo animations and edited them in NLA Editor. I want to make small tweaks here and there and add them to the whole animation but it doesnt work. When I rig up my character and animate it, it "erases" the whole underlying animation from mixamo. The animations are all fbx files. 

Do you know how to combine mixamo animations with own animations?
You have to keyframe the influence of IK (or other controls from your rig- for example, I have my hand and foot bones copy transforms from my respective hand and foot controllers) down to 0 for the Mixamo actions. Just go to every single Mixamo animation at the frame 0 and keyframe every custom influence/bone constraint to 0. You also have to do the reverse for your custom animations.
This approach works perfectly for exporting animations to Unity. I don't know how you're going to be using NLA editor so I can't say if it's going to work for you.