Cobalt

Ethereal Sight. The spider can see 60 feet into the Ethereal Plane while on the Material Plane and vice versa.

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 the spider knows the location of any other creature in contact with the same web.

Multiattack.
The spider makes two attacks with its bite.

• Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target.
  Hit: 19 (3d10 + 4) piercing damage. Once per day one of your bite attack can poison a creature. The target must make a DC 16 Constitution saving throw, taking 27 (6d8) poison damage on a failed save or half as much on a successful one. If the poison reduces the target to 0 hit points, the target is stable but paralyzed for one hour.

Ethereal Jaunt (Enhanced).
As a bonus action, the spider can magically shift from the Material Plane to the Ethereal Plane or vice versa. While on the Ethereal Plane, it can see and hear the Material Plane. It can also attack creatures on the Material Plane while remaining on the Ethereal Plane. Attacks of this type can only happen once per day.

Poisonous Aura.
Can be activated or deactivated as a bonus action. At the start of each of the spider’s turns, any creature the spider chooses within 10 feet of it must make a DC 16 Constitution saving throw or take 14 (4d6) poison damage. A creature that succeeds on the save is immune to this aura for 1 minute.