Savageborn Hydra

Double strike on a variable-sized body is the design conceit here: every point of power swings twice, so each +1/+1 counter you stack converts directly into two points of combat damage. That doubling is the whole appeal, but it does not bend the scaling into anything exotic; it just steepens the slope, turning an X-cost beater into something that hits for 2X the moment it can attack. The casting cost is where most of the work happens, since the initial X buys counters at a flat rate and is plainly the cheapest way to load the creature up. The sorcery-speed pump is the restriction that keeps the threat honest. You cannot pour mana in at instant speed to dodge a removal spell or to ambush a blocker mid-combat, so the creature grows only on your own turn, on your own clock, and the opponent always gets a window to answer it before the counters compound out of reach. Strip that limit away and this is a flash-grown finisher that demands an instant answer the turn it lands; with it, the card is a board presence you commit to over several turns, each counter a permanent investment that double strike then cashes at twice its face value. It punishes half-measures, too: shaving a point of toughness barely registers against a body this size, though a single bounce wipes the entire stack of counters and sends the whole investment back to your hand.