Harbinger of Night

A symmetrical attrition engine wearing a spirit's frame, and the symmetry is what gives the design its teeth. The upkeep trigger does not target, does not discriminate by color or controller, and shrinks every body on the board including this one, which is why the 2/3 stat line matters: it banks enough toughness to survive a couple of its own ticks while everything smaller dies first. The clock runs on a timer it cannot stop, so the deckbuilding question it asks is not "how do I protect this" but "how do I outlast it." The cleanest answers sit outside the creature column entirely (planeswalkers, enchantments, noncreature engines that keep advancing while the board erodes), or in creatures whose toughness banks against the accumulation. The card runs on a school of black sweeper that punishes go-wide boards without a single instant of input from the caster: lay it down, and the battlefield deflates a counter at a time on its own schedule. That patience is also its vulnerability, since the trigger waits for your upkeep rather than firing on entry, handing the table a full turn cycle to deploy a threat that can race the decay or simply remove the harbinger before its first tick lands.