Tiamat

When Tiamat drops to 0 hit points or dies, her body is destroyed but her essence travels back to her domain in the Nine Hells, and she is unable to take physical form for a time.

If Tiamat fails a saving throw, she can choose to succeed instead.

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.

Tiamat's weapon attacks are magical.

Tiamat 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.

Tiamat regains 30 hit points at the start of her turn.

Tiamat can use her Frightful Presence. She then makes three attacks: two with her claws and one with her tail.

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

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

Each creature of Tiamat'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.

Melee Attack Roll: +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).

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.

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.

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.

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.

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.

Tiamat can innately cast the following spell, her spellcasting ability is Charisma (spell save DC 26):

3/day: divine word