Magic Nails are nails with the power to weaponize whatever they are used on. Finn is shown to have at least five magic nails in "His Hero." He uses two of them, one to fix Fine Lady's shoe heel and one to "fix" Lumpy Space Princess' body. The magic nails were used in an attempt to help people non-violently by making them capable of defending themselves, so Finn apparently knew that they turned whatever they were used on into weapons. The magic nails have the same appearance of normal nails.