Celestial Cloud Dragon

Innate Spellcasting. The Celestial Cloud Dragon spellcasting ability is Charisma (spell save DC 16). It can innately cast the following spells, requiring only verbal components:

At will: detect evil and good, detect magic, detect thoughts, [Tooltip Not Found]

3/day each: bless, create food and water, cure wounds, lesser restoration, protection from poison, sanctuary, shield

1/day each: dream, greater restoration, scrying

Magic Weapons. The CCD weapon attacks are magical.

Shielded Mind. The CCD is immune to scrying and to any effect that would sense its emotions, read its thoughts, or detect its location.

Cloud Walk. Once per week, the CCD can choose to travel by itself or with it's rider to a "place between the clouds".  This operates similar to a teleport but with no chance of failure.  The CCD simply flies into a nearby cloud and flies out of a cloud near its destination.  This travel is instantaneous and the only drawback is that the rider will be disoriented for 1-2 minutes while acclimates to its new surroundings.

Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one creature. Hit: 8 (1d6 + 5) piercing damage, and the target must succeed on a DC 16 Constitution saving throw or be poisoned for 24 hours. Until this poison ends, the target is unconscious. Another creature can use an action to shake the target awake.

Constrict. Melee Weapon Attack: +8 to hit, reach 15 ft., one large or smaller creature. Hit: 10 (2d6 + 5) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the CCD can't constrict another target.

Change Shape. The CCD magically polymorphs into a humanoid that has a challenge rating equal to or less than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the CCD choice).

In a new form, the CCD retains its game statistics and ability to speak, but its AC, movement modes, Strength, Dexterity, and other actions are replaced by those of the new form, and it gains any statistics and capabilities (except class features, legendary actions, and lair actions) that the new form has but that it lacks. If the new form has a bite attack, the couatl can use its bite in that form.

As a bonus action, the CCD can choose to "Cloud step" up to 50' in any direction with it's rider (up to 300 lbs) as long as the destination can be seen and will not require passing through a solid object.  This bonus action can be performed no more than 4 times/day.