Adult Cobalt Dragon

Earth Flight. As part of a Cobalt Dragon's movement, it may enter the ground and move through it as if flying.

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

Multiattack. The dragon makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 14 (2d10+4) piercing damage.

Claw. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 8 (1d8+4) slashing damage.

Boulder Breath. The dragon vomits a series of Small boulders (minimum of 2) (Projectile 1-4+1) (3 ft. Sphere) at a point it can see or feel within its Tremorsense. The first creature in the line must make a DC 20 Dexterity saving throw. On a failed save, the creature takes 5 (1d8) bludgeoning damage and it is pushed backwards 5 ft. The creature must repeat the saving throw for each boulder until it succeeds. On a successful save the creature takes no damage and uses no movement to evade the line, forcing the creature behind it to attempt the saving throw. This deals double damage to objects and structures.

Spellcasting (Earth Magic). The dragon casts one of the following spells, requiring no spell components and using Wisdom as the spellcasting ability (spell save DC 20). To cast them the dragon must be standing on earth or stone. Each spell is cast at its lowest level.

2/day each: earth tremor, spike growth, erupting earth, wall of stone, earthquake

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

Earthen Tomb (2/Long Rest). The dragon can create a cocoon of Earth around itself, and heals by 4 hit dice at the end of every turn it remains inside said cocoon. The dragon cannot take any actions, bonus actions, or reactions inside the cocoon and has a movement speed of 0, but maintains awareness of surroundings via its Tremorsense. The cocoon has an AC of 14, and a health pool of 1/2 (rounding up when necessary) the dragon's HP when summoned.

The dragon can take 3 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.

Claw. The dragon makes one claw attack.

Earth Magic (Costs 2 Actions). The dragon uses Earthen Tomb or Spellcasting.