The Mightstone and Weakstone [The Brothers' War Prerelease Promos] Skyridge It has "Sacrifice this creature:

It has "Sacrifice this creature: Add C

Set: Unknown Event Type: Creature — Bird Rarity: Common Cost: {3}{U} Flying

While you control "Duel Dragon Token"

+1: Up to one target land you control becomes a 3/3 Elemental creature with vigilance

Set: Black & White: Dragons Exalted Type: Psychic Rarity: Promo Retreat cost: Colorless

The Mightstone and Weakstone [The Brothers' War Prerelease Promos] Skyridge It has "Sacrifice this creature:Set: The Brothers' War Prerelease Promos Type: Legendary Artifact Powerstone Rarity: Rare Cost: {5} When The Mightstone and Weakstone enters the battlefield, choose one Draw two cards. Target creature gets 5 5 until end of turn. {T}: Add {C}{C}. This mana can't be spent to cast nonartifact spells. (Melds with Urza, Lord Protector.)