Cloudkill is a uncommon Sorcery card from Commander Legends: Battle for Baldur's Gate (CLB), collector number 121. Current market price: $0.17 (foil $0.25), TCGplayer market prices via Scryfall.
All creatures get -X/-X until end of turn, where X is the greatest mana value of a commander you own on the battlefield or in the command zone.
All Commander Legends: Battle for Baldur's Gate cards and prices