Phase Spider

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

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

The spider ignores movement restrictions caused by webbing.

and the target must make a DC 11 Constitution saving throw, taking 18 (4d8) 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.