Blood Mist

Double strike doled out on a repeatable trigger lives and dies by what it doubles, and the trigger that powers it fires only at the beginning of combat on your turn: cast it in your precombat main phase and it goes to work the same turn, pinning the doubling onto a single attacker of your choosing the moment combat begins. That sets the strategic axis: this is not a finisher you point at the biggest creature on the board, it is an engine you point at whatever creature carries the most rider value. Deathtouch turns the doubled swing into a two-for-one in combat math; lifelink makes each attack a doubled life swing; trample or a damage-based trigger gets its number run twice. The trigger recurs every turn the enchantment survives, which separates it from a one-shot pump: it lives through the combat step it powers, so the doubling renews each of your turns as long as you have a creature worth dressing up. The cost of that consistency is that the trigger only fires on your turn, asks you to already have a board worth doubling, and leaves a window between your combats for an opponent to remove either the enchantment or the chosen creature. It is a build-around in the older sense: a permanent that rewards a deck constructed to feed it the right target, rather than a card that improves any board it joins.