Unpredictable

Self-taught fighter, Dirty fighter, Street fighter, or applicable background.

You’ve developed your own unique style of pugilism. You gain the following ability:

• If you are already in combat, as a bonus action you make a feign attack
• On the next round, you can make one unpredictable strike (advantage on attack roll on a creature)
• You must describe in detail the maneuver intended, specify a particular target (not in defensive alert) 
• (examples: sucker punch, headbutt, windpipe, trip, pin, push, disarm, etc.)
• can apply either Dex or Wisdom modifier