does unity have any way to play an animation mirrored

So i was rewatching this video http://www.gdcvault.com/play/1020583/Animation-Bootcamp-An-Indie-Approach

About 5.25

He mentions making a running animation with just two keyframes (reach and pass)
I'm trying that myself, but i've quickly come to the realisation that i can't seem to do it with any less than five.
Reachleft, pass, reachright, pass again, reachleft again

If i play the animation with pingpong, i can reduce it to three, but still

That's quite a bit more, and will be a pain to work with. I wonder if there's an easier way?
Technically, these two frames DO contain all the data we need, i just need a system to handle it. What i basically want to do is pingpong the animation, playing it forward first, and then in reverse AND mirrored. Then forward, then reverse mirrored again, etc.

Is this even possible to do in unity?
NB: I am using the humanoid rig, which should at the least, make it a very possible feature to implement, if it isnt already.

 

really ? arg, ive been wondering why i couldn't find it ;-;

please implement that in future D: