Amalgamasque

Legendary Resistance (6/Day). If the Amalgamasque fails a saving throw, it can choose to succeed instead.

Regenerate Regains 20hp at the start or its turns.

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

Reflective Carapace. Any time the Amalgamasque is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1 to 5, the tarrasque is unaffected. On a 6, the Amalgamasque is unaffected, and the effect is reflected back at the caster as though it originated from the Amalgamasque, turning the caster into the target.

Siege Monster. The Amalgamasque deals double damage to objects and structures.

Antimagic Cone. The Amalgamasque central eye creates an area of antimagic, as in the antimagic field spell, in a 300-foot-cone. At the start of each of its turns, the Amalgamasque decides which way the cone faces and whether the cone is active. The area works against the Amalgamasque  own eye rays.

Avoidance. If the Amalgamasque is subjected to an effect that allows it to make a saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Turn Immunity. The Amalgamasque is immune to effects that turn undead.

Multiattack. The Amalgamasque can use its Frightful Presence. It then makes five attacks: one with its bite, two with its claws, , one with eye ray, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +19 to hit, reach 10 ft., one target. Hit: 36 (4d10 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the tarrasque can’t bite another target.

Claw. Melee Weapon Attack: +19 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Tail. Melee Weapon Attack: +19 to hit, reach 20ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Frightful Presence. Each creature of the Amalgamasque's choice within 120 feet of it and aware of it must succeed on a DC 17 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with disadvantage if the Amalgamasque is within line of sight, 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 the Amalgamasque's Frightful Presence for the next 24 hours.

Swallow. The Amalgamasque makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite’s damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the tarrasque, and it takes 56 (16d6) acid damage at the start of each of the

1.  If the Amalgamasque takes 60 damage or more on a single turn from a creature inside it, the Amalgamasque must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the Amalgamasque. If the Amalgamasque dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

 If the Amalgamasque takes 60 damage or more on a single turn from a creature inside it, the Amalgamasque must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the Amalgamasque. If the Amalgamasque dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 30 feet of movement, exiting prone.

Chorus of Liches The amalgamasque central eye is that of a beholder stalks have their eyes replaced by the skulls of demiliches. An amalgamasque has 10 demiliches, they cannot move on their own ad instead move with the amalgamasque, ans are considered part or the amalgamasque, but act independently on their own initiative and track their own hip points(120 20d4 +40 ) Use the demilich stat blockwith the following changes Howl works in a 120ft cone with and the frightened condition last until the target succeeds the saving throw at the end of its turns. Life drains works within range of the amalgamasque blindsight, and heals both the demilich and the amalgasasque.  Each demilich also has the Eye Ray of a beholder.                                                                                                                                                                              

Howl (Recharge 5–6). The Amalgamasque emits a bloodcurdling howl. Each creature within 120ft cone of the Amalgamasque that can hear the howl must succeed on a DC 15 Constitution saving throw or drop to 0 hit points. On a successful save, the creature is frightened until the end of its next turn.

Life Drain. The Amalgamasque targets up to three creatures that it can see within 10 feet of it. Each target must succeed on a DC 19 Constitution saving throw or take 21 (6d6) necrotic damage, and the demilich regains hit points equal to the total damage dealt to all targets.

Eye Rays. The Amalgamasque shoots three of the following magical eye rays at random (reroll duplicates), choosing one to three targets it can see within 120 feet of it:

1. Charm Ray. The targeted creature must succeed on a DC 16 Wisdom saving throw or be charmed by the beholder for 1 hour, or until the Amalgamasque harms the creature.
2. Paralyzing Ray. The targeted creature must succeed on a DC 16 Constitution saving throw or be paralyzed 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.
3. Fear Ray. The targeted creature must succeed on a DC 16 Wisdom saving throw or be frightened 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.
4. Slowing Ray. The targeted creature must succeed on a DC 16 Dexterity saving throw. On a failed save, the target’s speed is halved for 1 minute. In addition, the creature can’t take reactions, and it can take either an action or a bonus action on its turn, not both. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
5. Enervation Ray. The targeted creature must make a DC 16 Constitution saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one.
6. Telekinetic Ray. If the target is a creature, it must succeed on a DC 16 Strength saving throw or the Amalgamasque moves it up to 30 feet in any direction. It is restrained by the ray’s telekinetic grip until the start of the beholder’s next turn or until the beholder is incapacitated.
   If the target is an object weighing 300 pounds or less that isn’t being worn or carried, it is moved up to 30 feet in any direction. The Amalgamasque can also exert fine control on objects with this ray, such as manipulating a simple tool or opening a door or a container.
7. Sleep Ray. The targeted creature must succeed on a DC 16 Wisdom saving throw or fall asleep and remain unconscious for 1 minute. The target awakens if it takes damage or another creature takes an action to wake it. This ray has no effect on constructs and undead.
8. Petrification Ray. The targeted creature must make a DC 16 Dexterity saving throw. On a failed save, the creature begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is petrified until freed by the greater restoration spell or other magic.
9. Disintegration Ray. If the target is a creature, it must succeed on a DC 16 Dexterity saving throw or take 45 (10d8) force damage. If this damage reduces the creature to 0 hit points, its body becomes a pile of fine gray dust.
   If the target is a Large or smaller nonmagical object or creation of magical force, it is disintegrated without a saving throw. If the target is a Huge or larger object or creation of magical force, this ray disintegrates a 10-foot cube of it.
10. Death Ray. The targeted creature must succeed on a DC 16 Dexterity saving throw or take 55 (10d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.                                                                                                         

The Amalgamasque can take 6 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 Amalgamasque regains spent legendary actions at the start of its turn.

Attack. The Amalgamasque makes one claw attack or tail attack.

Leap .  The Amalgamasque leaps, moving up o half its speed.If it ends the movement in  the air ,it falls or can grab a surface within reach that can support its weight to climb.

Chomp (Costs 2 Actions). The Amalgamasque makes one bite attack or uses its Swallow.

Eye Ray. The Amalgamasque uses one random eye ray.

Crypt Breath (Costs 2 Actions). The amalgamasque exhales a torrential cloud of sickening dust in a 60 ft cone that last 3 rounds. Creatures that start or end their turn in the area of dust take poison and necrotic damage equal to the amalgamasque constitution modifer (10 10, for 20). The area is heavily obscured a DC 15 Constitution saving throw or be blinded. A creature that succeeds on the saving throw is immune to this effect until the end of the demilich’s next turn.

Insidious Curse (Costs 3 Actions). The  Amalgamasque targets one creature it can see within its blindsight.. The target must succeed on a DC 20 Wisdom saving throw or be supernaturally cursed. Until the curse ends, the target's maximum health is reduced by the amalgamasque constitution modifer(10)at the start of each turns. Lost HP regained at  a rate of 10 per completed long rest.While cursed,the target has disadvantage on attack rolls and saving throws. The target can repeat the saving throw at the end of each of its turns, ending the curse on a success.