Pact of the Blade

At the beginning of your upkeep, you may create
a Legendary equipment artifact named Pact
Weapon, it has "Equipped creature is a warlock
in addition to its other types and," {2}, Discard a
card: Counter target spell that targets equipped creature and Equip {2}.
This goal is achieved when an opponent is
knocked out by a creature equipped by
Pact Weapon.