This is reminiscent of Faithless LootingFaithless Looting and its ilk
Anytime you tap a Swamp for mana, you add an extra black mana to your mana pool
You can verify it based on the symbols in the bottom right corner of the card (circle standing for Common, star for Rare, and so on) or use an online database
Number 0 Language English Legal Formats Commander, Legacy, Pauper, Vintage Not Legal Formats Alchemy, Brawl, Competitive Brawl, Historic, Modern, Pioneer, Standard, Timeless Rulings (10/4/2004) Cost reducers can be used to reduce the X part of the mana cost
Missing Card or Card Not Found These errors happen when the game cant find a card in your decklist