Dagger Mastery (revised)

You have mastered the dagger and know how to use this inconspicuous weapon in such a way as to bypass armored enemies' protection. You gain the following benefits:

• If you attack a large or smaller Creature who is utilizing some form of visible armor (both wearable armor and natural armor such as a carapace or shell), you can thrust your dagger into the gaps of their armor, bypassing it. If you make a melee dagger attack against a creature who is grappled, has not yet had a turn in combat, or if you have advantage on the attack roll, their AC is reduced by your proficiency bonus for that attack. 
• Before you make a Melee attack with a dagger you can choose to take a -2 penalty to the attack roll. If the attack hits, you add +4 to the attack's damage.