Chaxzar, Lord of Chains

Freedom of Movement. The Chaxzar ignores difficult terrain, and magical effects can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled.
Siege Monster. Chaxzar deals double damage to objects and structures.

Multiattack. Chaxzar makes three chain attacks, each of which it can replace with one use of Fling.
Bite. Melee Weapon Attack: +17 to hit, reach 5 ft., one target. Hit: 23 (3d8 + 10) piercing damage. If the target is a Large or smaller creature grappled by the Chaxzar, that creature is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside Chaxzar, and it takes 42 (12d6) acid damage at the start of each of Chaxzar's turns.

If the Chaxzar takes 50 damage or more on a single turn from a creature inside it, the Chaxzar must succeed on a DC 25 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of Chaxzar. If Chaxzar dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.
Chain. Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 20 (3d6 + 10) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained. Chaxzar has ten chains, each of which can grapple one target.
Fling. One Large or smaller object held or creature grappled by Chaxzar 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.
Metallic Storm. Chaxzar magically creates three bolts of liquid metal, each of which can strike a target the Chaxzar can see within 120 feet of it. A target must make a DC 23 Dexterity saving throw, taking 22 (4d10) necrotic damage on a failed save, or half as much damage on a successful one.

Chaxzar 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. Chaxzar regains spent legendary actions at the start of its turn.
Chain Attack or Fling. Chaxzar makes one chain attack or uses its Fling.
Metallic Storm (Costs 2 Actions). Chaxzar uses Metallic Storm.
Blood Cloud (Costs 3 Actions). Chaxzar expels an blood cloud in a 60-foot radius. The cloud spreads around corners, and that area is heavily obscured to creatures other than Chaxzar. Each creature other than Chaxzar that ends its turn there must succeed on a DC 23 Constitution saving throw, taking 16 (3d10) poison damage on a failed save, or half as much damage on a successful one. A strong current wind the cloud, which otherwise disappears at the end of the Chaxzar's next turn.