Adult Lurkyle

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

Oiled Body. The lurkyle is covered in large boils which ooze a thick foul-smelling acidic oil. Whenever the lurkyle is hit with a melee attack or hits a creature with a melee attack the creature gets covered in this oil and receives a point of Caustic Oil.

Pustular Boils. At the start of the lurkyle's turn, the boils on its body erupt covering each creature within 5ft in oil, creatures affected by this receive a point of Caustic Oil. 

Caustic Oil. At the end of each creature's turn, if it has one or more points of caustic oil on it, it takes 1d4 damage for each point of oil on it. It can use an action to remove all the points of oil on it.

Multiattack. A lurkyle makes two attacks: one with its bite and one with its stinger, or it makes a web attack.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 3) piercing damage and the target must make a DC 14 Constitution saving throw, taking 7 (2d6) points of poison damage on a failed save, or half as much damage on a successful one. 

Stinger. Melee Weapon Attack: +6 to hit, reach 5ft., one target. Hit: 9 (1d10 + 3) piercing damage the target must make a DC 16 Constitution saving throw, taking 12 (4d6) points of poison damage on a failed save, or half as much damage on a successful one. 

Acidic Web (Recharge 5–6). Ranged Weapon Attack: +5 to hit, range 30/60 ft., one creature. Hit: The target takes 11 (3d6) points of acid damage and is restrained. While restrained in this way the creature gets a point of Caustic Oil at the start of their turn. As an action, the restrained target can make a DC 14 Strength check, bursting the webbing on a success. The webbing can also be attacked and destroyed (AC 10; hp 5; vulnerability to fire damage; immunity to bludgeoning, poison, acidic, and psychic damage).