Is there a way to properly mirror an animation? I've already searched and searched and none of the answers to this question have helped me. I have an animation of a character moving right, and I need to flip it so that he's moving left. I've tried copying and pasting flipped both in the action editor and the 3D view and neither works right. My bone names are all correct with .L and .R for left and right respectively.

Any help would be greatly appreciated.

Here's the .blend file.
Add an Empty and place it in the same position where the origin point of your armature is. In Object Mode select your rig, then an Empty and press Ctrl+P.


Now select the Empty and scale it by -1 (S,X,-1).
Note that this may not be the proper way to do it. I think you should find the root bone (which controls all the other bones location) and rotate it by 180 degrees.