Exploding Borders is a common Sorcery card from Conflux (CON), collector number 106. Current market price: $0.25 (foil $0.23), TCGplayer market prices via Scryfall.
Domain — Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. Exploding Borders deals X damage to target player or planeswalker, where X is the number of basic land types among lands you control.