Noxious Hatchling

A four-mana 6/6 you can never actually cast as a 6/6: it walks in saddled with four -1/-1 counters, a 2/2 body nobody would pay four for on its own. The design pays itself off through the most ordinary thing your deck does. Every black or green spell you cast strips a counter, and four spells in its colors later the Elemental is fully grown. There is no mana tax, no sacrifice, no activation: the cost is simply playing the removal, ramp, and threats you were always going to cast, with the Hatchling fattening up as a free rider on a curve you never deviate from. Wither completes the thought, and the symmetry is the point. A creature crawling with -1/-1 counters is, thematically and mechanically, a creature that deals its damage in -1/-1 counters; the same mechanic that gates it on entry becomes its weapon once those counters are gone. Damage it deals in combat sticks as counters rather than washing off at cleanup, so anything that blocks it walks away permanently smaller. The marks that start as a handicap end as the threat.