Bebilith

Keen Smell. The bebilith has Advantage on Wisdom (Perception) checks that rely on smell.

Spider Climb. The bebilith can climb difficult surfaces, including along ceilings, without needing to make an ability check.

Rend Armor. If the bebilith hits a creature wearing armor with both Claw attacks on the same turn, it tears the armor apart: the armor takes a permanent and cumulative −1 penalty to the AC it offers. Armor reduced to an AC of 10 is destroyed. Damaged armor can be repaired by a smith.

Perishable Venom. Bebilith venom becomes inert, foul-smelling goo almost as soon as it touches air. It cannot be harvested or applied to weapons.

Multiattack. The bebilith makes one Bite attack and two Claw attacks. It can replace the Bite with a use of Web.

Bite. Melee Attack Roll: +11, reach 10 ft. Hit: 20 (3d8 + 7) Piercing damage. Constitution Saving Throw: DC 18, the target hit. Failure: 21 (6d6) Poison damage, and the target's Hit Point maximum decreases by an amount equal to the Poison damage taken. Success: Half damage only. The reduction lasts until the target finishes a Long Rest, and the target dies if its Hit Point maximum is reduced to 0.

Claw. Melee Attack Roll: +11, reach 10 ft. Hit: 14 (2d6 + 7) Slashing damage.

Web (4/Day). Dexterity Saving Throw: DC 18, one Gargantuan or smaller creature the bebilith can see within 30 feet. Failure: The target has the Restrained condition until the web is destroyed or the target escapes (Escape DC 18 as an action, using Athletics or Acrobatics). The web has AC 10, 14 HP, and Immunity to Poison and Psychic damage. Fire burns it away only on a roll of 1 on a d4, checked each round fire is applied.

Plane Shift. The bebilith casts Plane Shift on itself only, requiring no spell components. It can do so at will.