Vigilant Sentry

A 2/2 for three that asks you to fill your own graveyard before it does anything: below seven cards it is a plain body, and above it the static threshold ability flips on a +1/+1 and a repeatable combat lever. The activation is the part worth dwelling on. It taps for +3/+3, but only onto an attacking or blocking creature, which welds the buff to a combat step that has already begun. You cannot bait it out on an empty board or hold it up as a generic instant; you spend it once swings are declared and the math is sitting on the table, which makes it a repeatable trick you aim at the single most important point of combat each turn. This is the turn-the-corner design that the threshold archetype was built around: spend the early game dumping cards into the yard, then convert that count into a board-state engine that was dead weight a moment earlier. The Sentry is a pointed version of it, doing nothing for half the game and then producing aimable damage every turn it survives. The same gating is also the weakness. The pump is a tap ability, so the creature cannot swing and buff itself in the same combat, and a removal spell in response to the activation erases the body but the pump still resolves on a legal target.