Exterminator

You have pinpointed the weaknesses of foes many would not dream of encountering in combat. Your expertise gives you the following benefits:

• When you kill an Undead or Fiend that is at least one size below you, you get advantage on your next attack roll.
• You can use your knowledge to take half the amount of damage you would take if the enemy that damaged you was an Undead or Fiend that is at least one size below you. You can only do this once per either long or short rest.