Unholy Heat

The whole design lives in the gap between two damage and six. At two, this is a modest one-mana answer that trades down against anything with a real body: a spot-check for tokens and mana dorks and not much else. Turn delirium on, and it becomes one of the most efficient removal spells in the game, killing almost every creature that matters and reaching planeswalkers besides, all for a single red. The elegance is that the condition doing the scaling is one a fair deck fills incidentally: a fetchland, a cantrip, a creature, and a burn spell already put four distinct types under the yard's counter without asking the deck to bend around anything. That is what separates it from earlier conditional burn like Searing Blaze or Skewer the Critics, which demanded you satisfy a payoff at the moment of casting; here the requirement is a running total that a graveyard-agnostic tempo shell reaches on its own by the mid-game. It rewards exactly what a red-based fair deck already wants to run: cheap interaction, cheap threats, cheap card selection, each of which happens to be a different type. The downside is honest, since a fresh graveyard or a hand full of noncreature spells can leave you holding a two-damage spell when you needed six. But the ceiling is high enough, and the setup passive enough, that the floor rarely gets a vote.