Phase Spider is a Large monstrosity with unaligned alignment and Challenge Rating 3 in the 2014 SRD. This stat block includes AC 13, 32 hit points, speeds, traits, and actions.
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.