Shield of the Oversoul is a common Enchantment — Aura card from The List (PLST), collector number SHM-242. Current market price: $1.85, TCGplayer market prices via Scryfall.
Enchant creature As long as enchanted creature is green, it gets +1/+1 and has indestructible. (Damage and effects that say "destroy" don't destroy it. If its toughness is 0 or less, it still dies.) As long as enchanted creature is white, it gets +1/+1 and has flying.