As you progress you will unlock additional combos. These can be viewed by selecting the "scroll" in the top right corner. After completion of a level it will show numerous different attack moves however many of these appear to occur randomly depending on the enemy and the kill. The final combo viewable in the scroll menu unlocks after block 10-1. I am almost certain I did not do this combo yet still unlocked the achievement.
The attacks are either light or heavy (left/right sword button respectively). The final combo (a counterattack) in the list involves guarding first by pressing the "shield" button near the control pad then the jump button (this is the one that is not believed to be required).
The combos that appear to be required are as follows (all but the first two are visible in the scroll menu):
Light, Light, Light
Heavy, Heavy
Light, Light, Heavy
Light, Heavy, Heavy
Heavy, Heavy, Light
Block, Jump
All credit goes to AtlasShrugging1 from xbox360achievements.org
I unlocked this personally during 12-Something after I did a roundhouse kick which you unlock after Memory 10-1