Amethyst Dragon (Increased Threat)

Colossal. The dragon is one size category bigger then Gargantuan.

Innate Spellcasting (Psionics). The dragon’s spellcasting ability is Intelligence (spell save DC 25, +17 to hit with spell attacks). The dragon can innately cast the following spells, requiring no material components:

At Will: Blink, Control Water, Detect Magic, Dispel Magic, Freedom of Movement, Mage Hand (the hand is invisible), Protection from Evil and Good, Sending, Telekinesis, Thaumaturgy

3/day each: Forcecage, Globe of Invulnerability, Plane Shift, Reverse Gravity, Time Stop

Legendary Resistance (5/Day). If the dragon fails a saving throw, it can choose to succeed instead.

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

Magic Weapons. The dragon's attacks are considered magical.

Regeneration. The dragon regains 10 hit points at the start of each of its turns if it has at least 1 hit point.

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

Multiattack. The dragon makes four attacks: one with its Bite, two with its Claws, and one with its Tail.

Bite. Melee Weapon Attack: +17 to hit, reach 25 ft., one target. Hit: 25 (3d10 + 9) piercing damage plus 18 (4d8) force damage.

Claw. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (3d6 + 9) slashing damage. On a hit, if the target is Huge or smaller, it is grappled (escape DC 19) and is restrained until this grapple ends. The dragon has two claws, each claw can grapple one target at a time.

Tail. Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 22 (3d8 + 9) bludgeoning damage. On a Hit, the target must succeed on a DC 25 Strength saving throw. On a failed save, the target is knocked prone.

Singularity Breath (Recharge 5–6). The dragon creates a shining bead of gravitational force in its mouth, then releases the energy in a 150–foot cone. Each creature in that area must make a DC 25 Strength saving throw. On a failed save, the creature takes 81 (18d8) force damage, and its speed becomes 0 until the start of the dragon’s next turn. On a successful save, the creature takes half as much damage, and its speed is not reduced.

Change Shape. The dragon magically transforms into any beast or humanoid that is Large or smaller, while retaining its game statistics (other than its size). This transformation ends if the dragon is reduced to 0 hit points or uses its action to end it.

Psychic Bead. The dragon launches a bead of psychic energy towards one target in can see with 150 feet of it. The target must succeed on a DC 25 Dexterity saving throw. On a failed save, the target takes 36 (8d8) psychic damage.

Psychic Step. The dragon magically teleports, along with any equipment it is wearing and carrying, up to 60 feet to an unoccupied space it can see.

The dragon can take 5 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 dragon regains spent legendary actions at the start of each of its turns.

Attack. The dragon makes one Claw or Tail attack.

At–Will Spell. The dragon casts one of its “At–Will” spells, from its Innate Spellcasting list.

Detect. The dragon makes a Wisdom (Perception) check.

Teleport. The dragon uses its Psychic Step action.

Bite (Costs 2 Actions). The dragon makes one Bite attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 30 feet of it must succeed on a DC 25 Strength saving throw. On a failed save, a creature takes 19 (3d6 + 9) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Explosive Crystal (Costs 3 Actions). The dragon spits an amethyst that that explodes at a point it can see within 150 feet of it. Each creature within a 30–foot–radius sphere centered on that point must succeed on a DC 25 Dexterity saving throw. On a failed save, a target takes 22 (4d10) force damage and is knocked prone. On a successful save, a target takes half damage and is not knocked prone.