Hunters can sometimes instantly kill a foe by causing a critical hit. Some magical weapons that can be wielded by non-Hunters, such as the Death Dagger (Warrior, Rogue, Bard, Monk, Wizard) and Spectre Snare (Warrior, Bard, Wizard), can sometimes cause critical hits.
"The hunter can use most weapons, and has the ability (which grows with experience) to do critical hits in combat (i.e., to attack a nerve center or other vital area and instantly kill an opponent). A good skill."
Hunters critical chance seems to be 1 of 2 methods.
Method 1 is random 1-32 number per level which tops off at 255 (100%). If you average about 18 per level up you should reach max critical chance about level 16-22ish... give or take.
The other method is 1-3%+ 1% per dex over 14 to max of 99. Which means you want your hunters with high dex from the start.
Not exactly sure which method this apple game uses but I'd assume the first. (different systems use different methods). Either way, with a hunter with high dexterity you should get max criticals at level 20 or so, maybe sooner or later depending on RNG. (credit Steam user "EolSunder")