Trollhide is a common Enchantment — Aura card from The List (PLST), collector number M12-199. Current market price: $0.09, TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature gets +2/+2 and has "{1}{G}: Regenerate this creature." (The next time the creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)