溶(よう)鉄(てつ)の衝(しょう)撃(げき)

This sorcery deals 4 damage to target creature or planeswalker. If excess damage was dealt this way, note that excess damage, then you get a one−time boon with "When you cast an instant or sorcery spell, this boon deals damage equal to the noted number to target creature or planeswalker an opponent controls."