Magic Resistance.

The quavilithku has advantage on saving throws against spells and other magical effects.

Spider Climb.

The quavilithku can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Web Sense.

When in contact with a web, the quavilithku knows the exact location of any other creature in contact with the same web.

Web Walker.

The quavilithku ignores movement restrictions caused by webbing.

Actions

Multiattack.

The quavilithku makes two Bite attacks.

Bite.

Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 15 (2d10 + 4) piercing damage plus 17 (5d6) poison damage. If the target is a creature, it must succeed on a DC 18 Constitution saving throw or have the poisoned condition for 1 minute. While poisoned in this way, a creature can't regain hit points. A poisoned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Dissolving Web (Recharge 5–6).

The quavilithku expels acid-drenched webs in a 90-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 44 (8d10) acid damage on a failed save or half as much damage on a successful one. Nonmagical objects in the area that aren't being worn or carried take 44 (8d10) acid damage.

Bonus Actions

Assess Weakness.

The quavilithku sizes up a creature it can see within 40 feet of itself. Until the start of the quavilithku's next turn, it has advantage on attack rolls against the creature.

Quavilithku Spyder-Fiend