Mystic Snake

Counterspell trades one card for one card and leaves the table empty; this turns the same exchange into a 2-for-1 by stapling a 2/2 to the counter, so the answer and a permanent resolve in a single act. Flash is the joint that holds the two halves together: you hold up four mana like any reactive spell, wait for a spell worth answering, and on your opponent's turn cash the same mana into both a hard counter and a body. The design problem it answers is the one that has dogged countermagic forever, that a clean trade keeps you even on cards but never ahead on board; getting the spell and the creature in one motion was, and remains, a greedy thing to ask of . The price lives in the targeting clause. The trigger reads counter target spell with no exceptions, so a turn with an empty stack leaves you holding a 2/2 whose ability fizzles for want of a legal target, and the double-blue, single-green pip cost narrows the range of decks that can run it honestly. Bounce and reanimation made the body an engine almost immediately, since any way to flicker or replay it buys a fresh counter. That loop, and the refusal to make you pick between answering a threat and building a board, is why this snake became the template every later "tempo that does not fall behind" creature has been measured against.