Basilisk Gate

Every Gate before this one asked to be counted for flavor rather than function: they entered tapped, gained you a trifle of life, and otherwise sat in the manabase as a themed penalty you paid for the tribal joke. This is the card that gives the joke a payoff. Its first ability is the barest possible mana source, a colorless tap for one, which tells you the value was never meant to live there. The second ability is where the Gate count cashes in: a repeatable pump that scales with every Gate you have assembled, sorcery-speed so it can only turn a board into a threat rather than ambush a blocker or blow out combat. That timing restriction is doing real balancing work. A creature-boost that grows with a whole subtype's worth of lands would be oppressive at instant speed; confined to your main phase, it becomes a slow, telegraphed finisher that rewards the deck for having overcommitted to a land type most builders treat as a liability. What makes the design notable is the direction of the incentive: it retroactively justifies flooding your mana base with Gates, converting a deckbuilding cost into an accumulating win condition. The more your lands looked like a gimmick, the harder this one hits.