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

Drow Poison. The spider has a reservoir that is filled with drow poison. It applies drow poison each time it makes an adamantine fang attack, and does not need to apply the poison to its fangs to use drow poison.

Immutable Form. The spider is immune to any spell or effect that would alter its form. 

Magic Resistance. The spider has advantage on saving throws against spells and other magical effects.  

Magic Weapons. The spider's weapon attacks are magical.

Adamantine Plating. Any critical hit on the spider becomes a regular hit.

Multiattack. The spider makes two adamantine fang attacks. 

Adamantine Fang. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 4) piercing damage, and the creature must succeed on a DC 13 Constitution saving throw or be poisoned for 1 hour. If the saving throw fails by 5 or more, the creature is also unconscious while poisoned in this way. The creature wakes up if it takes damage or if another creature takes an action to shake it awake.