Ancient Mithral Dragon

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Innate Spellcasting. the dragon's innate spellcasting ability is Intelligence (spell save DC 21). It can innately cast the following spells, requiring no material components: at will: tongues 5/day each: counterspell, dispel magic, enhance ability

Mithral Shards. Ancient mithral dragons can choose to retain the mithral shards of their breath weapon as a hazardous zone of spikes. Treat as a spike growth zone that does 2d8 magical slashing damage for every 5 feet travelled.

Spellcasting. the dragon is a 15th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 21, +13 to hit with spell attacks). It requires no material components to cast its spells. The dragon has the following wizard spells prepared: cantrips (at will): acid splash, light, mage hand, minor illusion, prestidigitation 1st level (4 slots): charm person, expeditious retreat, magic missile, unseen servant 2nd level (3 slots): blur, hold person, see invisibility 3rd level (3 slots): haste, lightning bolt, protection from energy 4th level (3 slots): dimension door, stoneskin, wall of fire 5th level (2 slots): polymorph, teleportation circle 6th level (1 slot): guards and wards 7th level (1 slot): forcecage 8th level (1 slot): antimagic field

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 22 (2d12 + 9) piercing damage.

Claw. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 18 (2d8 + 9) slashing damage, and the target loses 5 hit point from bleeding at the start of each of its turns for six rounds unless it receives magical healing. Bleeding damage is cumulative; the target loses 5 hp per round for each bleeding wound it's taken from a mithral dragon's claws.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 20 (2d10 + 9) bludgeoning damage.

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 21 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of its turn, 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.

Breath Weapon (Recharge 5-6). A mithral dragon can spit a 60-foot-long, 5-foot-wide line of metallic shards. Targets in its path take 59 (17d6) magical slashing damage and lose another 10 hit points from bleeding at the start of their turns for 6 rounds; slashing and bleed damage is halved by a successful DC 21 Dexterity saving throw. Only magical healing stops the bleeding before 6 rounds. The shards dissolve into wisps of smoke 1 round after the breath weapon's use.

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

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 18 (2d8 + 9) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.