Basic Demon

Demonic Immortality. A demon cannot be killed without its head being fully sliced off from the rest of its body or being exposed to direct sunlight. 

Blood Art. Depending on the demon, it can use a special attack, spell, or cantrip. Every basic demon has 1 predetermined ability they can use without using mana or ki. This spell, cantrip, or special attack is determined at random. Because of the strength of a basic demon, this can only be up to a level 3 spell or cantrip, or a custom special attack. 

Bite. If a player character attacks within a 5-foot radius of the demon, it can attempt to bite the player character, forcing them to make a dex save. If failed, they take 1d4 poison damage, with an extra 1d4 at the start of every turn they make. If the demon is able to bite, it heals 1d6 for the demon as well. 

If the demon's health is depleted, but it hasn't reached any of its true death conditions, a legendary action will be taken.

Regenerate (Costs the demons turn). From when the demon's health is at 0 to when it is up again, it cannot move or fight back. If the demon survives to whatever attacked its turn, all damage is negated and it returns to full health.