well, i did this in my proyect check the images.
dropbox.com/s/xbztl89iqlhe5ph/Untitled.png
dropbox.com/s/cnfc75tx1bd8105/Untitled2.png
you need to create a variable like my hit_combo, so when you hit the button it ads 1 to that variable. you can use variable = 0 to show the animation of the first hit and then when variable = 1 show the animation of the second hit like the images you need to set hit_combo to 0 in the last hit of your combo.
sorry for my bad english.