Marshmist Titan is a common Creature — Giant card from Born of the Gods (BNG), collector number 76. Current market price: $0.11 (foil $0.17), TCGplayer market prices via Scryfall.
This spell costs {X} less to cast, where X is your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)