Stalker (5e Feat)
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Prerequisites: 16 or higher in Dexterity, Proficiency or Expertise in Perception.
Through trial and error, you've learned that a quiet step, a clear eye, and a plentitude of patience is all you need for a good kill.
You gain Proficiency in Stealth. If you are already proficient, you gain Expertise.
You gain the Stalk action.
One per turn, while in combat and you are hidden, you can choose to use the Stalk action to stalk a target that you can see within 120 Feet. The chosen target must succeed a Perception Check contested by your Stealth Check. If the target fails, you begin to stalk your target. For each following turn, you can continue to use your Stalk action to gain a bonus +2 to the attack and damage rolls against that target for each turn you stalk. For each additional turn you take to Stalk, you gain another +2 to each roll. If the target succeeds, you are revealed to the target, and you lose your stalking bonuses.
While stalking, you are completely concentrated on your target. As such, you cannot cast spells, nor concentrate on them, during the time which you are stalking.
The target can continue to roll Perception Checks against your Stealth Checks on each of its turns, until you attack, or the target spots you. You lose the bonus upon attacking the target or if you are detected before you can land a hit.
After 3 or more rounds of continuous stalking, you can choose to forgo your attack bonus so that your next successful attack against your target will count as a Critical Hit, instead of a normal. You keep the damage bonus. You cannot lose these bonuses through being detected, but can instead be lost through you or your target being knocked unconscious or killed before a successful attack is landed.