There's no reason why the hunters standard single throwing knife ability shouldn't instakill on headshot. Shoulder charges instakill, as well as handheld supernova. I cant be the only one who thinks this?
edit: and make the damn arc uppercut do more damage.
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Add a charge time to increase the damage. Allow hunters to hold their dagger in had and throw it a different way for the OHKO, say around the same time to activate SC and youd have it.