Mammoth Umbra is a uncommon Enchantment — Aura card from Planechase Anthology (PCA), collector number 10. Current market price: $0.24, 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.)