By exiling Hateflayer into Agatha's Soul Cauldron and granting its untap-activated ability to Yurlok of Scorch Thrash, Yurlok gains the explosive means to repeatedly target itself and untap. Heartstone steps in to discount this activation cost, making the loop exceptionally cheap to sustain. As Yurlok churns out endless mana for everyone using its own ability, any unspent mana left floating at the end of phases turns Yurlok of Scorch Thrash's static life-drain punishment into a lethal finisher for your opponents.