Mammoth Umbra is a uncommon Enchantment — Aura card from Rise of the Eldrazi (ROE), collector number 37. Current market price: $0.26 (foil $0.39), TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature gets +3/+3 and has vigilance. Umbra armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)