War Elemental

The triple-red cost is the first warning that this is a snowball payoff wearing a creature's clothes, and the sacrifice clause is the second: cast it on an empty board with no damage dealt this turn and it kills itself on arrival, a 1/1 that never gets to swing. It follows your aggression rather than starting it. The crucial wrinkle is that the counter ability only fires while the Elemental is already on the battlefield, watching the turn unfold; it has no memory of damage dealt before it resolved. So the burn spell that cleared its sacrifice condition does nothing to grow it. The body that lands is a 1/1, and it only balloons from the damage that comes after: the next bolt to the face, every subsequent point the opponent takes while it sits in play, including the Elemental's own combat damage, which feeds it directly the moment it connects. Note what does not count: paying life to crack a fetchland or pay an upkeep cost is loss of life, not damage, and the ability is strict about the distinction. This is a closer for a deck already winning the damage race, not a card you want to draw early. The triple pip prices the ceiling, and the sacrifice clause gates entry: in any deck not already pouring damage at the opponent's face, this is a blank. It scales with everything the deck throws downstream, so it pays off momentum already in motion rather than generating it.