Cataclysm

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.

Siege Monster. Cataclysm deals double damage to objects and structures.

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

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

Unstoppable. Cataclysm is immune to effects that would alter its form or movement such as the petrified condition or spells like hold monster.

Terrifying Presence. Any creature that starts its turn within 120 feet of Cataclysm and is aware of it must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Cataclysm's Terrifying Presence for the next 24 hours.

Multiattack. Cataclysm makes two slam attacks.

Slam. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 32 (4d10 + 10) bludgeoning damage.

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 33 (4d10 + 10) piercing damage.

Soul Drain. Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: The target is grappled (escape DC 18). While grappled in this way, the target takes 33 (6d10) necrotic damage at the start of each of its turns as Cataclysm drains its life force. Cataclysm regains hit points equal to the necrotic damage dealt, and the target's hit point maximum is reduced by an amount equal to one-fourth of the necrotic damage dealt (rounded down). This reduction lasts until it is removed by a Wish spell.

Necrotic Crush. Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: The target is grappled (escape DC 18). While grappled in this way, the target takes 28 (8d6) bludgeoning damage plus 28 (8d6) necrotic damage at the start of each of its turns. If the creature has been grappled for more than 2 rounds, their movement speed maximum will lower by 10 for each round after that. This reduction lasts until the target finishes a long rest.

Fling. One Large or smaller object held or creature grappled by Cataclysm is thrown up to 60 feet in a random direction and knocked prone. If a thrown target strikes a solid surface, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 18 Dexterity saving throw or take the same damage and be knocked prone.

Cataclysmic Crush. Cataclysm chooses a point it can see within 120 feet of it. All creatures within a 20-foot radius of that point must make a DC 27 Dexterity saving throw. On a failed save a creature takes 55 (10d10) bludgeoning damage and is knocked prone. On a successful save, the creature takes half as much damage and isn't knocked prone.

Charge. If Cataclysm moves at least 20 feet straight toward a target and then hits it with a slam attack on the same turn, the target takes an extra 14 (4d6) bludgeoning damage. If the target is a creature, it must succeed on a DC 18 Strength saving throw or be knocked prone.

Unleash Fury. Cataclysm can make one additional slam attack as a bonus action.

Deathly Touch. Cataclysm reaches out with its deathly touch. One creature it can reach must succeed on a DC 18 Constitution saving throw or take 10 (3d6) necrotic damage.

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

Unyielding. In response to being hit by a melee attack, cataclysm can make one melee attack with its slam.

Retaliation. When Cataclysm takes damage form a creature that is within 5 feet of it, it can use its reaction to make a melee weapon attack against that creature.

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

Attack (Costs 1 Action). Cataclysm makes one slam attack.

Move (Costs 1 Action). Cataclysm moves up to half its speed.

Chomp (Costs 2 Actions). Cataclysm makes a bite attack.

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.