Winter's Night

Snow lands turn into ramp under this enchantment, but the engine bites every hand at the table: tap a snow source and it produces an extra mana of the type it already made, then sits tapped through its controller's next untap step. The symmetry is the entire design. There is no quiet way to abuse it; you reap the upside only by skewing the snow-land count heavily in your favor, ideally with a manabase that wants the burst more than it minds losing those lands for a turn. The World subtype layers a second restriction on top: only one World permanent can exist at a time, so a second copy or a mirror match doesn't double the effect but instead sends the older one to the graveyard. That fragile uniqueness clause wrapped around a symmetrical Howling Mine-style engine is the high-variance, build-around design Alliances traded in, dating from the period when snow was an Ice Age land-type mechanic rather than a tribal payoff. The reward was genuine, but the deckbuilding tax (commit to snow, accept that your opponents share the ramp, and protect a permanent that any duplicate destroys) was steep enough that most tables left it alone.