[@Skallagrim]
Another big downside of a reverse guillotine is that it's over handed instead of underhanded. You could take the elbow pretty easily and twist the arm away. Without the other hand for grip and stability it's kind of weak. 

And you could go for underarm and gut punches to break his grip. Which would break pretty easily since he won't have had a chance to breathe since the liver punch.

Other readily available responses are illegal moves, since there are now blows to the back of the head, back of the neck or spine. So my response will have to be entirely leg and left arm, which is where you have me at a disadvantage.

I've got an idea and I'm keeping it on the back burner until I figure this out.