Cursed of Tharizdun

Legendary Resistance (3/Day). If the Cursed fails a saving throw, it can choose to succeed instead.

Magic Resistance. The Cursed has advantage on saving throws against spells and other magical effects.

Marshal Undead. Unless the Cursed is incapacitated, it and undead creatures of its choice within 60 feet of it have advantage on saving throws against features that turn undead.

Spellcasting. The Cursed is a 19th-level spellcaster. Its spellcasting ability is Charisma  (spell save DC 18, +10 to hit with spell attacks). The Cursed has following paladin spells prepared:
1st level(4 slots): command, compelled duel, searing smite

2nd level (3 slots): hold person, magic weapon                                           

3rd level (3 slots): dispel magic, elemental weapon                                                    

4th level (3 slots): banishment, staggering smite                                                     

5th level (2 slots): destructive wave (necrotic)  

Multiattack. The Cursed makes three longsword attacks.

Longsword. Melee Weapon Attack: +11 to hit, reach 5 ft., 1 target. Hit: 9 (1d8 + 5) slashing damage, or 10 (1d10 + 5) slashing damage if used with two hands, plus 18 (4d8) necrotic damage, and the target must make a DC 18 Wisdom saving throw or gain one random form of short-term madness. 

Invoke Madness (Recharge 6). One creature within 30 feet of the Cursed must make a DC 18 Wisdom saving throw or gain one random form of long-term madness.     

Parry. The Cursed adds 6 to its AC against one melee attack that would hit it. To do so, the Cursed must see the attacker and be wielding a melee weapon.

The Cursed 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 Cursed regains spent legendary actions at the start of its turn.

Attack. The Cursed makes a longsword attack.

Invoke madness (Costs 2 Actions). The Cursed uses Invoke Madness.

Summon Spawn (Costs 3 Actions). The Cursed summons 5 spawns of madness.