Callous Exploiter

Whenever Callous Exploiter deals combat
damage to a player, inscribe. (Create a Pact token.
It's an artifact with "{4}, Sacrifice this artifact: Draw
a card. This ability costs {1} less to activate for each
other creature or Pact you've sacrificed this turn.")
Whenever you activate an ability of a Pact, if
exactly one mana was spent to activate that
ability, each opponent loses 3 life and you gain
3 life.