Underdark Scout

The Underdark Scouts train their abilities until perfection, and forgo all connection to magic. Or in instances where Magic is either rare or doesnt exist, they dont need it anyways. Instead they use their own wits and training to take down their enemies. 

Snapshot

After years of firing your bow or throwing your knives, you become attuned to the motion so well that you can deal more damage with a single action. Whenever you make an attack with a ranged weapon you are proficient in, you can choose to take a -5 penalty to the Attack roll. On a hit, treat it like a critical hit, and roll double the damage dice you normally would. 

Undetectable

You've become so skilled at stealth craft that when you make an attack while hiding, you don't alert anyone to your location. 

Uncanny Wits

You've focused on honing your mind to a point where you find it easier to search people's emotions, as well as your surroundings. You can tell the true intentions of creatures much easier, recall info about monsters and other enemies you find, and you are more thorough when searching rooms for clues. It is also harder to sneak up on you. You gain proficiency in Investigation, Insight, Survival and Perception.  in the even that you are already proficient in one or more of these skills, you don't get to choose any more.

Underdark Training.

You have inept abilities from your training. Whenever you make an ability check with a skill you're proficient in, or an attack roll with a weapon of which you are proficient, you can expend a spell slot to add a modifier equal to 1 plus the level of the slot expended. 
Or as a reaction, you can gain the same bonus to your AC, and this bonus lasts until you're next turn. 

Enhanced Stealth

Your training was more than just your mind, but your skills in stealth craft as well. You gain proficiency in stealth, and whether you have it already or not, you gain expertise in stealth, allowing you to add twice your proficiency bonus when you use this skill.