Colossus of Akros

Eighteen mana is the number this thing is really asking for. Eight buys an indestructible 10/10 wall that legally cannot attack; the payoff sits behind another ten-mana activation, at which point monstrosity resolves, places ten +1/+1 counters, turns the body into a 20/20, hands it trample, and lifts the defender restriction so it can finally swing. That is a two-stage payment by design, and the first stage is insurance rather than pressure: a body that shrugs off nearly every sweeper while you assemble the mana to wake it up. Monstrosity was an era's chosen framing for the top-end mana sink, a way to make a big creature matter on arrival and again much later by paying into an activated ability rather than a cast-once ETB, but few of its bearers went as far as ten counters in a single activation. Bolting that figure to indestructibility narrows what can answer it: damage-based sweepers and combat leave it standing, so opponents are pushed toward the outs indestructibility ignores, namely exile, bounce, or a -X/-X large enough to zero the toughness. The reward for that patience is a finisher that ends things in a swing or two. It is deliberately clumsy by the standard of efficient closers, and the clumsiness is thematic: a colossus is supposed to take forever to stand up.