This requires you to perform all the combos for each character listed in the pause menu. These are the knockback, stun, uppercut, backlash, various rush moves and so on. Hope this helps.
Edit- The last combo for each character is unlocked at level 22. Also you do not have to perform all of them on an enemy, most can be done in any of the towns.
It seems as though the uppercut followups for the Mage and Ranger require an enemy to mark complete.