Melee Weapon Master

You've learned to put the skill of training with single handed weapons to your advantage. You gain the following benefits: 

• On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
• Before you make a melee attack with a melee weapon that you are proficient with, you can choose to take a -1, -2 or -3 penalty to the attack roll. If the attack hits, you add +2 to +6 to the attack's damage (based on the  penalty, +2 for -1, +4 for -2, or +6 for -3).