How do you kill things with mortal blow tier 2 hp challenge

You'll need to proc the instakill effect of mortal blow. Get a mob below half health (or lower if not maxed) and then attack it at point blank

 

to add to this, it's 10% chance to proc.

My strategy was: attack a high HP mob until it's HP is < 50% and facehug it and attack till it dies. Took me about 400 HP potions (barbarian elixir) at Shaolin 1-2F

 

Alternatively, equip a shitty low level bow and take off all your equips and facetank weaker mobs to save pots