Sunken Palace

A tapped Island is the floor here, and the ceiling is a spell doubler bolted onto your manabase. The second ability carries the whole design: pay two mana and exile seven cards from your graveyard, and the blue mana it produces comes with a copy rider, so the next spell or activated ability it helps cast gets duplicated with new targets. That structure hides a real cost behind a familiar shape. Seven cards is a steep graveyard tax, steep enough that the payoff only comes online after a game has run long enough to fill the yard, and the copy attaches to the mana rather than the spell, so you have to spend that specific mana on the thing you want doubled. The reward is that it copies anything short of another mana ability: a game-ending sorcery, an activated ability on a permanent already in play, an instant that answers a threat twice over. Note the boundary the wording draws: it duplicates spells and activated abilities, not triggers, so the doubling has to be something you cast or activate on purpose, not a battlefield event that happens to fire. Building the copy into a land rather than a spell is the real wrinkle: the doubling costs no card and occupies no slot beyond the land drop you were already making, which is why the graveyard exile has to be as punishing as it is. It is a value-engine land pretending to be fixing, waiting on a graveyard deep enough to justify the detonation.