Serebii.net Header
Study, An ability that makes certain Pokémon unhittable by Moves which are One Hit KOs. Firstly, Here's a List of all Pokémon Who Can Have This Ability:

 

Now These are the attacks that offer one hit KOs, Aswell as the details of them

Name PP Att. Acc. Type Effect Contest Type Appeal Jam
Fissure 5 - 30
Causes foe to faint
Guillotine 5 - 30
Causes foe to faint; the lower the foe's level is than yours, the better accuracy comes; can't hit higher
Horn Drill 5 - 30
Causes foe to faint
Sheer Cold 5 - 30
Causes Foe to faint; the lower foe's level is than yours, the better Accuracy becomes; can't hit higher