Lavafume Invoker
A board that has stopped trading on the ground needs somewhere to dump a long game's worth of accumulated mana, and this Goblin is built to be that outlet: a near-vanilla body carrying one prohibitively expensive switch that only comes online deep into a game. The Invokers all share that shape, but this one's payoff is the most aggressive of the set: a battlefield-wide +3/+0 swing that converts a stalled attack step into a lethal one. The restraint here is structural rather than imposed. There is no finality counter or once-per-turn clause keeping it in check, because the activation cost is the leash; you will rarely fire it twice, and the card is not built to ask you to. What pays for the effect is the opportunity cost of holding that much mana open for a single offensive turn, which is exactly why this class of card rewards patience without ever pressuring the early game. The 2/2 contributes almost nothing to the plan it enables; it is a placeholder on the ground while the mana accrues, then a single flip, late and decisive, that ends a game the smaller bodies could not.
