This is how to quickly decapitate Uke I am unsure if I am the original creator but I found this while playing Toribash myself:

Hold All (C)
Extend Abs
Raise Both Shoulders
Grab Both Hands (V)
Space X 2.

Contract Both Pecs
Lower Both Shoulders
Contract Abs
Space (Just keep pressing until you decap Uke).

This move is easy to counter if you want to make an awesome replay then follow these steps.