Avedeus

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

Radiant Hyperabsorption. Whenever the dragon is subjected to radiant damage, it takes no damage and instead regains a number of hit points equal to double the radiant damage deal

Glyph of Invulnerability. The glyph is a construct that sits in the dragon's forehead. It has 100 hit points, and an AC of 30. It automatically succeed on all saving throw and have the evasion ability.

Immutable Form. The dragon is immune to any spell or effect that would alter its form.

Material Anchor. The dragon cannot be teleported against its will.

Ethereal Aegis. If the dragon takes below 10 damage, from any source, it redirects the damage to whoever dealt it. If no one directly dealt the damage, the dragon casts thunderwave, without expending a spell slot. If it is in Broken form, it now redirects everything below 20 damage, and the thunderwave triggered by taking damage, not dealt by anyone directly, is now cast at spell level 3.

Dragonrush. The dragon can expend a 5th level spell slot, to increase its movement speed to 5500ft, until the end of the round. Every time the dragon moves, it, as well as all creatures grappled by it takes 1d100 force damage. All fall damage dealt to the dragon and all creatures grappled by it is multiplied by 1d20, if the dragon is using this ability, while the fall damage is dealt.

Infinite Influx. If the dragon dies, it is instead merely stunned, and loses all traits and proficiencies, but this trait. Furthermore, it gains five levels of exhaustion, these levels cannot be increased nor reduced. It remains like this for 1d10 minutes, being reincarnated as a dracolich of its former self, when that has past. It expends all remaining spell slots, restoring 10 * the spell's level (minimum of five) hit points, per spell slot lost. When it is reincarnated, all exhaustion is cured and it regains its traits and proficiencies. This trait can be removed with a wish spell, only if the dragon is stunned by this trait.

Arcane Cinder. The first cantrip the dragon casts each turn does not expend an action or bonus action.

Spellcasting. The dragon is an 20th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 26, +18 to hit with spell attacks). The dragon has the following spells prepared:

Cantrips (at will): fire bolt, prestidigitation, true strike, shocking grasp, (all cantrips if Aggravated Essence is active)

1st level (4 slots): detect magic, thunderwave, shield, magic missile, sleep*, chromatic orb*

2nd level (3 slots): web, hold person, scorching ray, misty step invisibility*, warding wind*

3rd level (3 slots): hypnotic pattern, counterspell, dispel magic, glyph of warding, gaseous form*, sleet storm*

4th level (3 slots): polymorph, banishment, watery sphere*, dimension door*

5th level (3 slots): wall of force, etherealness, hold person*, conjure elemental*

6th level (1 slot): disintegrate, contingency, globe of invulnerability*, wall of force*

7th level (1 slot): symbol, forcecage, crown of stars*, reverse gravity*

8th level (1 slot): dominate monster, sunburst, mind blank*, feeblemind*

9th level (1 slot): meteor swarm, wish*

With Aggravated Essence activated, it has twice the amount of spell slots.

Spells with a * is spells only usable with Aggravated Essence.

Scales of Immortality (Intact Form Only). The dragon is immune to all damage, except for lightning, psychic, fall damage and thunder damage. If the glyph of invulnerability is destroyed, the dragons maximum hit points is reduced by 100, at the end of each round. If it is reduced to 0 hit points in this way, it is destroyed, dying despite Infinite Influx.

Wrath of the New Might (Broken Form Only). If a spell or ability shoots out multiple projectiles, such as eldritch blast, magic missiles, prismatic barrage or scorching ray, the amount of projectiles is tripled.

Arcane Momentum (Broken Form Only). The dragon is permanently under the effects of the haste spells

Hasty Reflexes. The dragon can take three reactions per round.

Grappler. The dragon have advantage on attack rolls it is grappling. Furthermore, it can use its action to try to pin a creature grappled by it. To do so, make another grapple check. If it succeeds, it and the creature is both restrained until the grapple ends.

War Caster. The dragon has advantage on Constitution saving throws made to maintain concentration on a spell, when it takes damage. Furthermore, when a hostile creature's movement provokes an opportunity attack from it, it can use its reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Spell Sniper. When it cast a spell that requires it to make an attack roll, the spell's range is doubled, and when its ranged spell attacks ignore half cover and three-quarters cover. 

Keen Mind. It always know which way is north, and always knows the number of hours before the next sunset or dawn. Furthermore it can accurately recall anything it has heard or seen within the past month.

Alert. It gain a +5 bonus to initiative and can't be surprised while conscious. Furthermore, other creatures don't gain advantage on attack rolls against it as a result of being unseen by it. 

Crusher. Once per turn, when it hits a creature with an attack that deal bludgeoning damage, you can move it 5 feet to an unoccupied space, provided the target is no more than one size bigger than you, and when it score a critical hit that deals bludgeoning damage to a creature, attack rolls against that creatures are made with advantage until the start of its next turn.

Cursed Essence. If a creature of CR/level 3 or above is killed by the dragon, the creature vaporizes and a guardian of faith appears where they died. The guardian is the dragon's, and if it is dispelled the guardian is now controlled by the dead creature. This guardian does not disappear after dealing 60 damage, but disappears only after 8 hours or the destruction of Avedeus. 

Reflective Scales (Intact Form). Any time the dragon 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 dragon is unaffected. On a 6, the dragon is unaffected, and the effect is reflected back at the caster as though it originated from the dragon, turning the caster into the target.

Pure Havoc. The dragon deals double damage to objects and structures, as well as creatures of small size, or smaller.

Radiant Relocation (Essence). At the end of the dragon's turn, it can teleport to an unoccupied location it can see, within 120ft.

Might of Essence (Essence). The amount of spell slots available to the dragon is doubled. It can also use two cantrips, without using an action or a bonus action, at the start of its turn, instead of one.

Surge of Essence (5/day) (Essence). On the dragon's turn, it can take an additional turn. This can only be used once per round.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws. If it is in broken form it uses Frightful Presence, followed up by six attacks; one with its bite, four with its claws and one with its tail.

Bite. Melee Weapon Attack: +17; to hit, reach 30 ft., one target. Hit: 21(2d10 + 10); piercing damage plus 14 (4d6) fire damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6+10) slashing damage. If this is not used as a part of a multiattack, the dragon can force a creature hit by this attack to make a DC 21 Strength saving throw, being grappled if they fail.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.

Sweep of Void (Essence). Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) true damage. It is impossible to have immunity, resistance or vulnerability to true damage.

Resistance Drain (Essence). The dragon forces a creature to make a DC 27 Charisma saving throw. If it fails, the dragon can chose a damage type and remove the creature's resistance to that damage type, if it has any. If it has immunity, it is replaced by resistance. If it has absorption, it is replaced by immunity. If it does not have resistance nor immunity, it gains vulnerability. This ability can be used as a bonus action, on a grappled target.

Ethereal Realm (Essence)(Recharge 6). The dragon sends itself and a creature within 120ft. to the ethereal realm, as if casting etherealness. For the next d4-1 (minimum of 1) rounds, the dragon and the targeted creature is stuck in the ethereal realm. If a creature want to exit prematurely, it must succeed on a DC 27 Intelligence (Arcana) check. This check can be repeated each rounds.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 30 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 the dragon's Frightful Presence for the next 24 hours.

Fire Breath (Recharge 5–6). The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 29 Dexterity saving throw, taking 91(26d6) fire damage on a failed save, or half as much damage on a successful one.

Illuminating Beam (Recharge 6). The dragon unleashes its magic in a 10ft. wide, 1 mile long, line. Any creature in that area must succeed on a DC 23 Dexterity saving throw, taking 500 (6d100+197) radiant damage on a failed save, and 63 (6d20) fire damage on a successful one. The dragon can change the damage type from radiant, to any non-physical damage type, but it loses the damage dealt on a successful save. The dragon can use fire breath as a bonus action, after using this.

Prismatic Armageddon (Recharge 10) (Broken Form). The dragon uses its Illuminating beam, but can move the line. All creatures in up to ten, 10ft, 1 mile long lines must succeed on a DC 23 Dexterity saving throw, taking 500 (6d100+197) radiant damage on a failed save, and 63 (6d20) fire damage on a successful one. The beam moves from line to line as it tries to kill everything. The GM determines the collateral damage done by the beams. Until the start of its next turn, the dragon takes double damage, and lose the ability to take legendary actions. A creature cannot be affected by multiple lines. The dragon can change the damage type of the beam, to any damage type that is not bludgeoning, piercing and slashing. 

Prismatic Barrage. Tiny white missiles appear from the cracks and gaps in the dragon's scales. It creates 5 darts, of prismatic light. Each dart hits a creature the dragon can see, dealing 1d6+3 damage of the dragon's choice, to the hit creature.

Ethereal Clip (Intact Form Only). If the dragon takes an amount of damage that would be fatal to it, it can cast etherealness on itself. If it does so, it negates the damage that would be fatal, and is able to hold concentration for up to 1d4 rounds. This cannot be used if the dragon is below 300 hit points.

Shed Immortality. If the glyph of invulnerability is destroyed, it can change its form to Broken Form. When it does so, it can change the area it can see, in any way it'd like. This will often be in form of small motes of levitating earth, spikes risen from the earth, impaling those who'd be unlucky enough to fall, and lots of unstable mountainsides. This can be used as a free action, at the start of the dragons turn, if no reactions were available when the glyph was destroyed.

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 its turn.

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

Move. The dragon moves up to its movement speed.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Attack (Costs 2 Actions). The dragon makes a bite or claw attack.  

Spellsteal (Costs 3 Actions) The dragon forces a creature it can see to make a DC 21 Charisma saving throw. If it fails, it looses its highest level spell slot, and the dragon regains a spell of the same level.

Instantaneous Spell (Costs 0-5 Actions). The dragon casts a spell, from any spell list, without expending a spell slot. The cost of this action is determined by the spell level. The spell can be of 5th level or down. Using a cantrip does not cost an action, but can only be used thrice per round.