Due Diligence is a common Enchantment — Aura card from Murders at Karlov Manor (MKM), collector number 14. Current market price: $0.13 (foil $0.10), TCGplayer market prices via Scryfall.
Enchant creature When this Aura enters, target creature you control other than enchanted creature gets +2/+2 and gains vigilance until end of turn. Enchanted creature gets +2/+2 and has vigilance.