Ambusher. The drake has advantage on attack rolls against a creature it surprised.

Poisoning Absorption. When the drake is poisoned, any hit points it heals and any damage it deals is increased by its Wisdom modifier.

Legendary Resistance (1/Day). If the drake fails a saving throw, it can choose to succeed instead.

Strange Nature. The drake does not require food or drink.

Multiattack. The drake makes three melee attacks or two ranged attacks. 

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 14 (2d10 + 3) piercing damage plus 7 (2d6) acid damage.

Tail. Melee Weapon Attack: +4 to hit, reach 10 ft., one target. Hit: 12 (2d8 + 3) bludgeoning damage.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 12 (2d8 + 3) slashing damage.

Acid Spit. Ranged Weapon Attack: +4 to hit, range 20/50 ft., one target. Hit: 22 (4d10) acid damage and the target must make a DC 17 Constitution saving throw or have their Armor Class decreased by 2, or by 1 on a successful save. If the target has it's AC decreased to -2 less than its max AC and is wearing armor, the creature's armor gets a permanent -1 penalty. If the creature's armor gets a -5 penalty, it is destroyed by acid and cannot be repaired normally.

Poisonous Acid Breath (Recharge 5-6). The drake exhales toxic acid in a 35-foot cone. Each creature in that area must make a DC 16 Constitution saving throw, taking 19 (3d12) acid damage plus 6 (1d12) poison damage and be poisoned for 1 hour on a failed save, or half as much damage and only be poisoned for the next 1 minute on a successful save.