Lifetap

A pure sideboard enchantment from the era when Magic believed hate cards should target specific colors of mana, not specific strategies. The Circles of Protection were the template (single-color damage prevention bottled into one white enchantment), and Lifetap is the blue cousin: a hoser keyed to the opponent's basic land type rather than their game plan. The design assumes a world where "playing green" and "tapping Forests" are nearly synonymous, which was largely true at printing and has eroded with every fetchland, shockland, and dual cycle since. The trigger is also passive in a way modern design has moved away from: no activated cost, no choice, no decision point, just incidental life every time the green player does the thing they were going to do anyway. That makes it a curiosity now, but it preserves how early Magic conceived of color hate. The same generation gave us Karma for Swamps, Flashfires for Plains, and Tsunami and Boil for Islands. Lifetap is the gentlest of the cousins, trading the scorched-earth payoff of the others for a slow drip, and it is the only one that pays you for the opponent's normal play rather than punishing it. The lineage from here runs toward the modern "whenever an opponent does X" triggered enchantments that turn an opponent's routine into your engine.