Adult Spider Dragon

Legendary Resistance (3/Day). If the spider dragon fails a saving throw, it can choose to succeed instead.

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

Web Sense. While in contact with a web, the spider knows the exact location of any other creature in contact with the same web.

Web Walker. The spider ignores movement restrictions caused by webbing.

Multiattack. The dragon can use its Frightful Presence. It then makes five attacks: one with its bite and four with its claws.

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: (2d10 + 8) piercing damage, and the target must make a DC 11 Constitution saving throw, taking (2d6) poison damage on a failed save, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: (2d6 + 8) piercing damage.

Wings. Melee Weapon Attack: +14 to hit, reach 10 ft., two targets. Hit: (3d6) piercing damage.

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: (2d8 + 8) bludgeoning damage.

Frightful Presence. Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 15 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the dragon’s Frightful Presence for the next 24 hours.

Acidic Web (Recharge 5-6). The spider dragon shoots a web over a 25-foot area. Each creature in that area must make a DC 15 Constitution saving throw, taking (10d6) acid damage on a failed save, or half as much damage on a successful one, the target is restrained  by webbing. As an action, the restrained target can make a DC 15 Strength check, bursting the webbing on a success or taking (2d4+2) acid damage on a fail, if the restrained creature doesn't attempt to escape it also takes (2d4+2) acid damage. The webbing can also be attacked and destroyed (AC 10; hp 5; vulnerability to fire damage; immunity to bludgeoning, poison, and psychic damage). The web on the floor is difficult terrain and any creature that walks on it takes (2d4+2) acid damage.

The spider dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The spider dragon regains spent legendary actions at the start of its turn.

Detect. The spider dragon makes a Wisdom Perception check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon two attacks with its wings.