Flood

A repeatable tapper built into an enchantment shell, which in 1994 was a genuinely novel place to put the effect. The economics are the whole pitch: pay one mana once to establish it, then pay two blue per activation to keep a single ground creature from ever attacking or blocking. That recurring cost is the design discipline, the thing that keeps a permanent lockdown ability from being a one-card Pacifism: the more creatures the opponent commits to the board, the worse Flood's mana math gets, since you can only neutralize one per activation and only on the turns you can spare the blue. The "without flying" clause draws the other obvious line, exempting the exact creatures a blue deck would most want to ground. What it represents is early Magic's habit of pricing recursion in repeated mana rather than counters or charges: the same structural job a tap-down does today through evasion-stopping creatures or one-shot removal, Flood does by asking you to fund the tax turn after turn. As a piece of color-pie history it is a clean statement of where blue's tempo tools lived before the language of "flash" and "instant-speed interaction" was codified, an enchantment that wants to sit on the table and slowly drain your mana in exchange for keeping the board honest.