When you cast this spell, the blood used for the component congeals and grows to create a Shadowy visage of the original creature. The original creature can be a maximum of Medium size and, of course, must have blood (DM's interpretation).

The Shadow is summoned in a space adjacent to the caster, and shares all the same base stats -- including size, ability scores, movement speed, hit points, and AC -- as the original, cannot be healed, and doesn't gain benefits from racial or class features, and armor or magic items, though it does appear to wear or carry them.  It does, however, possess a mundane equivalent of any weapons or equipment which the original had on their person at the moment of Harvesting, and all weapons deal the normal damage for it's weapon type. All weapon attacks from the Shadow deal necrotic damage, and the Shadow cannot activate magic items or cast spells, though the caster can cast Touch spells through it using the normal rules for the spell. The Shadow counts as an Aberration, it's alignment is Chaotic Evil, and it is immune to poison and psychic damage, as well as mind-altering effects such as the Charmed effect.

As long as the caster maintains concentration, the Shadow follows it's summoner's every command to the best of it's ability and can be dispelled as a bonus action. But, if concentration is lost at any point, rather than being dispelled, the Shadow goes Berserk. On each of its turns while Berserk, the Shadow attacks the nearest creature it can see. If no creature is near enough to move to and attack, the Shadow will attack a nearby object, with preference for an object smaller than itself, or one which, if destroyed, would clear the way to the nearest creature it's aware of. Once the Shadow goes Berserk, it continues to do so until it is destroyed or the full duration is up. Concentration is also lost if the Caster wills the Shadow to travel beyond 60 feet from them.

Concentration saving throws must be made whenever you or the Shadow takes damage, as the Shadow becomes enraged and harder to control. The DC for maintaining concentration when the Shadow takes damage is equal to either the Shadow's Charisma ability score, or the damage taken; whichever is higher.