Misty Slithering. The serpent can move through a space as narrow as 1 inch without expending extra movement to do so.
Multiattack. The serpent makes one Bite attack and uses Constrict.
Bite. Melee Attack Roll: +6, reach 5 ft. Hit:8 (1d8 + 4) Piercing damage plus 3 (1d6) Cold damage.
Constrict. Strength Saving Throw: DC 14, one Medium or smaller creature the snake can see within 10 feet. Failure: 3 (1d6) Bludgeoning damage plus 7 (2d6) Cold damage. The target has the Grappled condition (escape DC 14), and it has the Restrained condition until the grapple ends.
Ephemeral, Heat-Draining Elemental