You have made a deal with the Father of Lies, Asmodeus, gaining you the following infernal benefits:

• You can speak, read, and write Infernal.
• When you reduce a hostile creature to 0 hit points, you gain temporary hit points equal to twice your proficiency bonus.
• You learn the command spell. You can cast this spell without expending a spell slot. Once you cast the spell in this way, you can’t cast it in this way again until you finish a long rest. You can also cast the spell using spell slots you have of the appropriate level.  You choose Intelligence, Wisdom, or Charisma as your spellcasting ability for this spell when you choose this feat. Fiends have disadvantage on the save.