Ancient Desert Spider

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

Web Walker: The spider ignores movement restrictions caused by webs, and it knows the location of any other creature in contact with the same web.

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

Reflective Carapace: Any time the ancient desert spider is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1, the ancient desert spider suffers effects as normal; on a 2 to 5, the ancient desert spider is unaffected. On a 6, the ancient desert spider is unaffected, and the effect is reflected back at the caster as though it originated from the ancient desert spider, turning the caster into the target.

Multiattack: The Ancient Desert Spider makes three attacks: one with its web and two bites.

Bite: Melee Weapon Attack: +15 to hit, reach 10 ft, one target. Hit: 26 (3d12 + 8) piercing damage and 10 (3d8) poison damage.

Web: Ranged Weapon Attack: Range: 120ft, Area: 60ft circle, Dexterity Saving Throw: DC 16. Webbing is shot at a creature that the spider can see within 120ft. The webbing explodes in a circle covering a 60 ft area. All creatures in this area must succeed a (DC 16) Dexterity saving throw or have the Restrained condition until the web is destroyed (AC 10; HP 5; Vulnerability to Fire damage; Immunity to Poison and Psychic damage).

Poison Breath (Recharge 5–6): The Spider exhales poisonous gas in a 30-foot cone. Each creature in that area must make a (DC 22) Constitution saving throw, taking 48 (16d6) poison damage or half as much on a success.

Ethereal Jaunt: As a bonus action, the spider can magically shift from the Material Plane to the Ethereal Plane, or vice versa.

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

Bite: Melee Weapon Attack: +15 to hit, reach 10 ft, one target. Hit: 26 (3d12 + 8) piercing damage and 10 (3d8) poison damage.

Web (Recharge 5–6): One creature the spider can see within 60 feet has webbing shot at them, they must succeed a (DC 13) Dexterity saving throw or get caught in the webbing. The target has the Restrained condition until the web is destroyed. (AC 10; HP 5; Vulnerability to Fire damage; Immunity to Poison and Psychic damage).

Poison Breath (Recharge 5–6): The Spider exhales poisonous gas in a 30-foot cone. Each creature in the area must make a (DC 22) Constitution saving throw, taking 48 (16d6) poison damage or half as much on a successful one.