Amulet of Kroog

Two mana to play, then a tap and two more mana to prevent a single point of damage to anything you choose: that ratio is a fossil from when one point of life was a meaningful unit of currency. The shape tells the whole story. There is no restriction on what gets protected, because the design assumed a world where Savannah Lions and Mons's Goblin Raiders define the curve and a single Lightning Bolt is the format's apex threat. Prevention shields from that era were priced against a damage economy modern Magic has long since inflated past; the same activation today would not blunt one relevant attacker, let alone the burn it was built to soften. The instinct on display is one Wizards has mostly retired: the artifact as a slow, grinding damage-prevention faucet, charging repeatedly to buy back fractions of life one activation at a time. Circle of Protection effects eventually absorbed the role in white, priced as enchantments rather than colorless artifacts, and the prevention-per-activation model gave way to replacement effects and lifegain that move whole points or chunks of life at once. What remains is the record of the older approach: a colorless, universally-targeted, pay-as-you-go shield built for a damage clock that ran slow enough to make a single prevented point feel like a transaction worth a turn's worth of mana.