The truly horrifying combo is Battlemaster+Gloomstalker+Thief with a couple specific hand crossbows and the sharpshooter feat. All that Dex + 15 AC from Yuan-Ti scale mail they sell at last light means 4 attacks per round each and 20+ AC.
Oh, and stealth, and lockpicking. Astarion? Never heard of him.
Had to use a bonus action for something? Then you've got battlemaster ranged moves to fear, trip, or disarm. It's disgusting.