Ancient Amuletor (HP)

This must be done with the wizard. While the kills track across all playthroughs and difficulties this one is a bit odd as a direct hit often won't kill an enemy on Normal or higher. As such I suggest playing on Easy and letting enemies stack up on a crystal once you have a skill available. When you are ready to fire hit the :Move: button on the left controller then the left to summon your ice orb, at this point throw it as you would the normal attack. This will kill mummies on 1-1 on Easy every time, so a couple of runs should be enough to make up any kills you may have remaining. I think some kills may count when the enemy is still under the skill's effect but don't count on those as you'll likely end up wasting quite a bit of time like I did. The 1-1 strategy is much quicker and definitely counts.