Arachnia

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

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

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

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 7 (1d10 + 2) piercing damage, 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.

Poison Web (Recharge 5-6). Ranged Weapon Attack: +7 to hit, range 20/40 ft., one creature. Hit: The target is restrained by webbing. As an action, the restrained target can make a DC 12 STR check, bursting the webbing on a success. The webbing can also be attacked and destroyed (AC 10; HP 5; vulnerability to fire damage; immunity to bludgeoning, poison, and psychic damage).
At the start of each of its turns, a restrained creature must make a DC 15 CON saving throw, taking (2d10) poison damage on a failed save or half as much damage on a success.