Sneak Attack Expert

Your proficiency with smaller weapons allows you to make deadlier sneak attacks.

• Weapons that have a base damage of 1d4 count as finesse weapons for you, if they don't already have that property.
• When you make a sneak attack with either a dagger, sickle, or ranged weapon with a base damage of 1d6 or lower, you may double the sneak attack dice.
• When you make a sneak attack with either a club or light hammer, after taking the attack damage, the opponent must make a constitution save.  The DC is 8+your proficiency bonus+your Str or Dex modifier.  If  the opponent fails they fall unconscious.  They can be awakened by being hit by an attack or another creature using an action to wake them.  If they pass the save then they are knocked prone.  If the sneak attack is made while the opponent is surprised or unware of your presence, then they have disadvantage when making the save.  You can choose to allow the opponent to pass the save.  Creatures that have a size of large and up are immune to these effects.

These abilities can be used a number of times equal to your proficiency bonus and replenish after a short or long break.  If the sneak attack is made while your opponent is surprised or unaware of your presence, then you can use this ability for free.