Titania

One static line of permission, granted for the whole game, that turns the one-land-per-turn rule (the most fundamental resource governor in Magic) into a soft suggestion. That is the entire avatar: no mana cost, no body to deploy, no upkeep, no clock. The Vanguard cards sat beside the battlefield rather than on it, each one rewriting a single rule from the opening hand: starting hand size, life total, or some play option that lasted the whole match. Titania's contribution is the cleanest possible expression of that brief, and also the one with the longest afterlife. The effect later became a template Wizards returned to on actual permanents: Exploration, Azusa, Lost but Seeking, and the various ramp commanders that hang a creature off the same line of text all descend from this idea of breaking the land-drop ceiling. What dates the avatar is precisely what makes it elegant. A free, permanent, downside-free engine for doubling your land development could exist in a format built around lopsided, splashy modifications nobody had to draw or cast. The moment that effect migrated into the main game, it got priced, conditioned, and bolted to a body. Here it just sits there and gives the land for nothing, which is a thing the printed game has never been willing to do since.