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

Spider Climb. Yasdriia can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Special Equipment. Yasdriia wields a brooch of living essence.

Multiattack. Yasdriia makes one Bite attack and two Claw attacks (Dragon form) or two Whip attack (Humanoid form).

Bite. Melee Weapon Attack: +13 to hit, reach 3 m., one target. Hit: 16 (2d10 + 7) piercing damage plus 11 (2d10) poison damage.

Claw. Melee Weapon Attack: +13 to hit, reach 1,5 m., one target. Hit: 17 (2d6 + 7) slashing damage.

Tail. Melee Weapon Attack: +13 to hit, reach 4,5 m., one target. Hit: 15 (2d8 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 21 Strength saving throw or be knocked prone.

Whip (Humanoid form). Melee Weapon Attack: +13 to hit, reach 3 m., one target. Hit: 9 (1d4+7) slashing damage plus 4 (2d4) psychic damage.

Nightmare Breath (Recharge 5–6). Yasdriia exhales a cloud of spores in a 27 m cone. Each creature in that area must make a DC 20 Wisdom saving throw. On a failed save, the creature takes 49 (9d10) psychic damage, and it is frightened of the dragon for 1 minute. On a successful save, the creature takes half as much damage with no additional effects. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Spellcasting. Yasdriia casts one of the following spells, requiring no spell components and using Charisma as the spellcasting ability (spell save DC 20):

At will: detect magic

1/day each: telekinesis, water breathing, passwall, command, faerie fire, detect thoughts, dissonant whispers

Change Shape. Yasdriia magically transforms into any creature that is Medium or Small , while retaining its game statistics (other than its size). This transformation ends if Yasdriia is reduced to 0 hit points or uses a bonus action to end it.

Yasdriia can take 3 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 dragon regains spent legendary actions at the start of its turn.

Commanding Spores. Yasdriia releases spores around a creature within 9 m of it that it can see. The target must succeed on a DC 20 Wisdom saving throw or use its reaction to make a melee weapon attack against a random creature within reach. If no creatures are within reach, or the target can’t take a reaction, it takes 11 (2d10) psychic damage.

Tail Attack. Yasdriia makes one Tail attack.

Spore Salvo (Costs 2 Actions). Yasdriia releases poisonous spores around a creature within 9 m of it that it can see. The target must succeed on a DC 20 Constitution saving throw or take 28 (8d6) poison damage and become poisoned for 1 minute. The poisoned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Whip Attack (Humanoid form). Yasdriia makes one Whip attack.

Spellcasting (Costs 2 Actions). Yasdriia uses Spellcasting.