Catastrophe

Protective of Calamitas. Catastrophe is highly protective of his sister, Calamitas. Any attempt to control his mind fails automatically unless the controller uses a Wish spell. This protection does not extend if the controller is Calamitas herself.

Undead Resilience. If damage reduces Catastrophe to 0 hit points, he must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, Catastrophe drops to 1 hit point instead.

Terrifying Presence. Any creature that starts its turn within 30 feet of Catastrophe must make a DC 23 Wisdom saving throw. On a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to Catastrophe's Terrifying Presence for the next 24 hours.

Multiattack. Catastrophe makes three melee attacks

Catastrophe's Sword. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 23 (4d6 + 9) slashing damage plus 18 (4d8) necrotic damage.

Grasping Hand. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: The target is grappled (escape DC 20). Until this grapple ends, the target is restrained and takes 21 (6d6) necrotic damage at the start of each of its turns.

Necrotic Surge. Catastrophe can use a bonus action to release a wave of necrotic energy. Each creature within 10 feet of it must make a DC 23 Constitution saving throw, taking 21 (6d6) necrotic damage on a failed save, or half as much damage on a successful one.

Sword Dance. Catastrophe can use a bonus action to perform a sword dance, making it more agile and precise. For the next minute, Catastrophe has advantage on Dexterity saving throws, its movement does not provoke opportunity attacks, and it gains a +2 bonus to its AC.

Dark Command. Catastrophe issues a command to a lesser undead creature within 60 feet that can see and hear him. The creature must use its reaction to follow the command on its next turn.

Calamitas' Protector (Recharge (5-6). If a creature Catastrophe can see targets Calamitas with an attack and Catastrophe is within 10 feet of Calamitas, Catastrophe can use his reaction to interpose himself. Catastrophe swaps places with Calamitas and becomes the target of the attack instead.

Vengeful Strike. If Catastrophe's younger sister, Calamitas, is attacked  within a range that Catastrophe can reach (up to 15 feet), it can use its reaction to make a melee attack against the attacker. This reaction can only be used if Catastrophe is within 30 feet of Calamitas.

Necrotic Absorption. When Catastrophe is subjected to necrotic damage, it can use its reaction to absorb the necrotic energy. Instead of taking necrotic damage, Catastrophe regains a number of hit points equal to the necrotic damage dealt.

Catastrophe 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. Catastrophe regains spent legendary actions at the start of its turn.

Attack (Costs 1 Action). Catastrophe makes one melee attack.

Move ( Costs 1 Action). Catastrophe moves up to half its speed without provoking opportunity attacks.

Call to Calamitas (Costs 3 Actions). Catastrophe calls out to its sister, Calamitas. If Calamitas is within 120 feet and able to hear Catastrophe, she can immediately use her reaction to teleport to an unoccupied space within 5 feet of Catastrophe.