Seal of Fire

The structural trick here is splitting a Shock into two phases. Pay the mana up front, leave the enchantment on the battlefield, and the damage becomes a free action later rather than a mana-tax decision in the heat of a turn. That timing shift is the whole appeal: you can tap out for a threat and still threaten removal, a tempo profile no instant matches, because the activation costs nothing once the Seal is down. The target stays open until you crack it, so you commit to nothing and the two damage can land on a creature, a planeswalker, or a face. The drawback is exposure. The threat goes public the instant the enchantment resolves, and a careful opponent will see it sitting there, play around two damage, and sequence so the sacrifice does as little as possible. You trade the open-mana tell for a different tell: a permanent that announces exactly what it will eventually do. The frame has resurfaced across eras whenever designers want burn that dodges the held-up-mana read, and this remains the cleanest version of the idea: a permanent whose only reason to exist is to become a burn spell once you decide to spend it.