The Seedcore is a rare Land — Sphere card from Phyrexia: All Will Be One (ONE), collector number 403. Current market price: $0.51 (foil $0.82), TCGplayer market prices via Scryfall.
{T}: Add {C}. {T}: Add one mana of any color. Spend this mana only to cast Phyrexian creature spells. Corrupted — {T}: Target 1/1 creature gets +2/+1 until end of turn. Activate only if an opponent has three or more poison counters.