Necron Overlord

The keyword is a euphemism, but the math underneath is real: Relentless March turns your artifact board into a repeatable drain, converting each untapped artifact into a point of life pried off an opponent. What makes the ability worth building around is that it double-taxes the battlefield. You pay generic mana, you tap the Overlord, and you tap X other artifacts, so a wide artifact array becomes ammunition rather than blockers or mana rocks doing their day jobs. The 2/5 body is deliberately defensive, not a beater: it wants to sit back and survive while the artifacts it presides over accumulate into a larger and larger burn spell. That is the tension the design resolves. A one-shot drain of any meaningful size would be a rate problem, so instead the effect is throttled by how much artifact investment you can afford to tap down on a given turn, and by the fact that tapping those artifacts costs you their own abilities for the turn. It rewards a board that is already deep in artifacts (Treasure, Clue, mana rocks, other Necrons) and punishes committing to the drain too early. The result is a slow, escalating inevitability engine: not a combo piece so much as a clock that ticks faster with each new piece of metal you can spare from the drain, so that a stalled table quietly becomes a lost one.