Nightstriker Serpent (5e Creature)
From D&D Wiki
Large monstrosity, neutral evil
Skills Perception +4, Stealth +10
Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 6 (1d4 + 4) piercing damage, and the target must make a DC 13 Constitution saving throw, taking 17 (5d6) poison damage on a failed save, or half as much damage on a successful one.
Nightstriker serpents are nocturnal ambush predators with scales as dark as the night sky and hearts just as dark. A nightstriker serpent's venom is considerably more potent than that of an ordinary snake, but by far the most terrifying thing about them is the fact that they seem to meld with ambient darkness, such that they are almost never seen by their victims until it is too late.