Serpentine is a rare Creature — Wurm card from Unstable (UST), collector number 120. Current market price: $0.31 (foil $0.43), TCGplayer market prices via Scryfall.
Landfall — Whenever a land you control enters, Augment {2}{G} ({2}{G}, Reveal this card from your hand: Combine it with target host. Augment only as a sorcery.)