Couatl

Constrict. Melee Weapon Attack: +6 to hit, reach 5 ft., one Medium or smaller creature. Hit: 14 (3d6 + 4) bludgeoning damage and the target is grappled (escape DC 14). Until this grapple ends the target is restrained the couatl can't constrict other targets and the couatl has advantage on attacks against the target.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage and the target makes a DC 14 Constitution saving throw. On a failure it is poisoned for 24 hours. The target is unconscious until the poisoned condition ends or a creature uses an action to shake the target awake.

Heal (1/Day). The couatl touches a creature magically healing 20 hit points of damage and ending the poisoned condition on that creature.

Shapeshift. The couatl magically changes its form to resemble that of a humanoid or beast or back into its true form. It reverts to its true form if it dies. If its form is humanoid it is equipped with clothing and a weapon. While shapeshifted its statistics are the same except that it can't use Constrict and Shielding Wing and it may gain a swim speed of 60 or lose its fly speed if appropriate to its new form. If its a beast it can use its bite attack. If its a humanoid it may make a weapon attack which functions identically to its bite attack.

Shielding Wing. When the couatl or a creature within 5 feet is attacked, the couatl can interpose a wing and impose disadvantage on the attack.