Otarian Juggernaut

Threshold turns this from a 2/3 with nowhere to go on offense into a 5/3 that has to swing every turn, and that compulsory-attack clause is the whole bargain. The Juggernaut creature type has carried a "must attack" tax since the original Juggernaut in Antiquities, and here it gets bolted onto a graveyard counter: the reward for filling your yard is a real clock, but the price is a creature you no longer control in combat. The "can't be blocked by Walls" line is the other piece of inherited Juggernaut design, a clause that has shipped with the type for decades even when, as here, it almost never matters in practice. The cleverest part is the timing of the flip. Below seven cards the artifact is a defensible blocker that sits back; the moment your graveyard tips over the threshold, it loses the ability to hold the ground it was defending and is forced forward, so the same card switches from wall to weapon based on a count you accumulate over the game rather than mana you spend in a single turn. That is threshold paying out exactly the way it should: rewarding the patient, graveyard-feeding deck with a payoff that scales to how committed it already is, while quietly stripping away the flexibility that made the low end worth running in the first place.