They blend into the distance before there arrow finds its mark. And it always does

proficiency

Starting at 3rd level, You gain proficiency in the Heavy crossbow, Light Crossbow, Shortbow and Longbow and perception checks.

Keen Eye

Starting at 3rd level, When an enemy is partially obscured your keen eye from hard practise picks up there figure as if they are not obscured. 

Snipers bolt

Starting at 9th level, If no enemy is within 15 feet of you your sneak attack die becomes a d12. at 10 feet or above its d8. You can use this feature a number of times equal to your wisdom modifier between long rest

Precision of the Trained

By 13th level,  you can spend 2 minutes preparing a deadly accurate shot at an enemy. You must remain stationary and must take no other action while preparing. If it hits the next shots wait time is halved. If it is cancelled or misses it remains the same.
either:
The attack does an extra 6d12
The targets AC becomes 8 + their dex for the duration of this attack
The shot is a guaranteed critical and deals an extra 6d4 damage

Master Archer

When you reach 17th level, you have become adept at targeting your enemies weak points. Spend an action preparing. If you hit then:
If they have below 100hp they die and you heal a number equal to your hit die maximum.
If above 100 hp they make a constitution save. On a fail they take 2d12 damage + 50 + Dex modifier + your level.
You can use this 3 times between long rests.