BEHOLDEMAT

Antimagic Cones. Each of the beholdemat's central eyes create an area of antimagic, as in the Antimagic Field spell, in a 150-foot cone. At the start of each of its turns, the beholdemat decides which way each cone faces and whether the cone is active. The area works against the beholdemat's own eye rays and spells.

Destructive Rebirth. When the beholdemat drops to 0 hit points or dies, it violently explodes in a 360-foot radius sphere of violent elemental and psionic energy centered on its body. Each creature in that area must make a DC 28 Constitution saving throw, taking 99 (22d8) acid damage, 132 (24d10) lightning damage, 115 (33d6) poison damage, 136 (39d6) fire damage, 108 (24d8) cold damage, and 135 (54d4) psychic damage on a failed save, or half as much damage on a successful one. If at least 1000 total hit points worth of damage were dealt in this way, the beholdemat is instantly revived at maximum hit points.

Innate Spellcasting (3/Day). BEHOLDEMAT can innately cast divine word (spell save DC 26). Her spellcasting ability is Charisma.

Freedom Of Movement. The beholdemat 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.

Legendary Resistance (5/Day). If BEHOLDEMAT fails a saving throw, she can choose to succeed instead.

Limited Magic Immunity. Unless she wishes to be affected, Tiamat is immune to spells of 6th level or lower. She has advantage on saving throws against all other spells and magical effects.

Magic Weapons. BEHOLDEMAT's weapon attacks are magical.

Multiple Heads. BEHOLDEMAT can take one reaction per turn, rather than only one per round. She also has advantage on saving throws against being knocked unconscious. If she fails a saving throw against an effect that would stun a creature, one of her unspent legendary actions is spent.

Regeneration. The beholdemat regains 50 hit points at the start of its turn.

Innate Spellcasting. The beholdemat's spellcasting ability is Charisma (spell save DC 26). The beholdemat can innately cast the following spells, requiring no material components:

At will: Bones of the Earth. Earthquake. Storm of Vengeance
5/day each: Divine Word, Dominate Person, Mass Suggestion, Wall of Fire 3/day each: Geas, Planar Binding 1/day each: Feeblemind. Power Word - Kill, Power Word - Stun
28 (+9)

Multiattack.  The beholdemat can use its Frightful Presence. It then makes four attacks: two with its claws, one with its tail, and one with its bite using one of its
heads

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 24 (4d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +19 to hit, reach 25 ft., one target. Hit: 28 (4d8 + 10) piercing damage.

Eye Rays. The beholdemat shoots five of the following magical eye rays at random (do not reroll duplicates), choosing one to five targets it can see within 240 feet of it:
1. Charm Ray. The targeted creature must succeed on a DC 26 Wisdom saving throw or be charmed by the beholdemat for 1 hour, or until the beholdemat harms the creature.

2. Paralyzing Ray. The targeted creature must succeed on a DC 26 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 26 Wisdom saving throw or be frightened for 1 minute. The target can repeat the saving throw at the end of each of it turns if it is at least 240 feet away from the beholdemat and can no longer see it, ending the effect on itself on a success.

4. Slowing Ray. The targeted creature must succeed on a DC 26 Dexterity saving throw. On a failed save, the target's speed is halved for 1 minute. In addition, the target 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 26 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 26 Strength saving throw or the beholdemat moves it up to 30 feet in any direction. It is restrained by the ray's telekinetic grip until the start of the beholdemat's next turn or until the beholdemat is incapacitated. If the target is an object weighing 300 points or less that isn't being worn or carried, it is moves up to 30 feet in any direction. The beholdemat 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 26 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 shake or slap it awake. This ray has no effect on constructs and undead.

8. Petrification Ray. The targeted creature must make a DC 26 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. If the targetd creature fails the initial saving throw by 5 or more, it is instantly petrified.

9. Disintegration Ray. If the target is a creature, it must succeed on a DC 26 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 26 Dexterity saving throw or take 55 (10d10) necrotic damage. The target dies if the ray reduces it to 0 hit points.

11. Telepathic Ray. The targeted creature must make a DC 26 Wisdom saving throw, taking 36 (8d8) psychic damage on a failed save, or half as much damage on a successful one. If the creature fails the save it is also stunned until the end of its next turn.

12. Chromatic Ray. The target creature must make a DC 26 Dexterity saving throw, taking 13 (3d8) acid damage, 22 (4d10) lightning damage, 17 (5d6) poison damage, 21 (6d6) fire damage, and 18 (4d8) cold damage on a failed save, or half as much damage on a successful one

Frightful Presence. Each creature of BEHOLDEMAT's choice that is within 240 feet of Tiamat and aware of her must succeed on a DC 26 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 Tiamat’s Frightful Presence for the next 24 hours.

Aberrant Chromatic Breath (Recharge 5-6). The beholdemat exhales elemental energies tainted with the power of the Far Realms through all five of its heads in a 180-foot cone. Each creature in that area must make a DC 27 Constitution saving throw, taking 67 (15d8) acid damage, 88 (16d10) lightning damage, 77 (22d6) poison damage, 91 (26d6) fire damage, 72 (16d8) cold damage, and 80 (32d4) psychic damage on a failed save, or half as much damage on a successful one.

The beholdemat can take 5 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The beholdemat regains spent legendary actions at the start of its turn.

Tiamat’s legendary action options are associated with her five dragon heads (a bite and a breath weapon for each). Once Tiamat chooses a legendary action option for one of her heads, she can’t choose another one associated with that head until the start of her next turn.

Bite. The beholdemat make a single bite attack.
Eye Ray. The beholdemat uses one random eye ray.

Bite. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 32 (4d10 + 10) slashing damage plus 14 (4d6) acid damage (black dragon head), lightning damage (blue dragon head), poison damage (green dragon head), fire damage (red dragon head), or cold damage (white dragon head).

Black Head: Acid Breath (Costs 2 Actions). Tiamat breathes acid in a 120-foot line that is 10 feet wide. Each creature in that line must make a DC 27 Dexterity saving throw, taking 67 (15d8) acid damage on a failed save, or half as much damage on a successful one.

Blue Head: Lightning Breath (Costs 2 Actions). Tiamat breathes lightning in a 120-foot line that is 10 feet wide. Each creature in that line must make a DC 27 Dexterity saving throw, taking 88 (16d10) lightning damage on a failed save, or half as much damage on a successful one.

Green Head: Poison Breath (Costs 2 Actions). Tiamat breathes poisonous gas in a 90-foot cone. Each creature in that area must make a DC 27 Constitution saving throw, taking 77 (22d6) poison damage on a failed save, or half as much damage on a successful one.

Red Head: Fire Breath (Costs 2 Actions). Tiamat breathes fire in a 90-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

White Head: Cold Breath (Costs 2 Actions). Tiamat breathes an icy blast in a 90-foot cone. Each creature in that area must make a DC 27 Dexterity saving throw, taking 72 (16d8) cold damage on a failed save, or half as much damage on a successful one.

Psychic Pulse (Cost 3 Actions). The beholdemat unleashes a burst of psionic energies in a 120-foot radius sphere centered on itself. Each creature in that area must make a DC 27 Wisdom save, taking 90 (36d4) psychic damage on a failed save, or half as much damage on a successful one.