Spellcasting. The Shadow Hand is an 14th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 18, +10 to hit with spell attacks). The Shadow Hand has the following wizard spells prepared:

Cantrips (at will): chill touch, encode thoughts, friends, minor illusion, shocking grasp

1st level (4 slots): cause fear, witch bolt, shield,

2nd level (3 slots): blindness/deafness, hold person, ray of enfeeblement

3rd level (3 slots): vampiric touch, counterspell, dispel magic, fireball

4th level (3 slots): greater invisibility, dimension door

5th level (2 slots): cone of cold, enervation

6th level (1 slot): disintegrate, flesh to stone

7th level (1 slot): finger of death

In Between Life And Death  The shadow hand is counted as both a humanoid and undead. Whenever this creature is targeted by an affect or spell it can choose whether it want to be considered humanoid or undead for the purposes of the spell or effect. So it might decide to be undead when targeted by a hold person spell but humanoid when targeted by turn undead or divine smite. This creature also doesn't ever need to sleep, drink or eat.

Empowering Shadows While in dim light or darkness this creature deals an extra 4d6 necrotic damage on melee spell and weapon attacks

Regeneration. The Shadow Hand regains 20 hit points at the start of its turn. If the Shadow Hand takes radiant damage, this trait doesn't function at the start of the Shadow Hand's next turn. The Shadow Hand dies only if it starts its turn with 0 hit points and doesn't regenerate.

Mind Corruption. Melee Spell Attack: +10 to hit, reach 5 ft., one creature. Hit: 6 (2d6) necrotic damage. The target must succeed on a DC 17 Wisdom saving throw or be Stunned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Multiattack. The Shadow Hand makes three attacks with its greatsword.

Greatsword. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 8) slashing damage.

The Shadow Hand can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Shadow Hand regains spent legendary actions at the start of its turn.

Shadow Shift  The Shadow hand moves up to its full movement. While in dim light or darkness it doesn't provoke opportunity attacks.

Cast Spell  The Shadow Hand casts a spell of 2nd level or lower (This still expends the spell slot).

Multiattack (Costs 2 Actions)  The Shadow Hand does its multiattack.

Corrupt Mind (Costs 2 Actions)  The Shadow Hand does its Mind Corruption.