Amphibious. The dragon can breathe air and water.

Sneak Attack (1/Turn). The dragon deals an extra 7 (2d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the dragon that isn't incapacitated and the dragon doesn't have disadvantage on the attack roll.

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (2d10 + 4) piercing damage plus 7 (2d6) poison damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Poison Breath (Recharge 5–6). The dragon exhales poisonous gas in a 30-foot cone. Each creature in that area must make a DC 14 Constitution saving throw, taking 42 (12d6) poison damage on a failed save, or half as much damage on a successful one.

Alter Shape. The dragon magically transforms into a rat, a raven, or a spy and retains its alignment, damage immunities, hit points, and Hit Dice, as well as its Intelligence, Wisdom, and Charisma scores. This transformation ends if the dragon is reduced to 0 hit points or if it uses another bonus action to end it.

Cunning Action. On each of its turns, the dragon can use a bonus action to take the Dash, Disengage, or Hide action.