Phase Spider
Large Monstrosity, unaligned
700 XP
Special Abilities
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.
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.
Quick Reference
Running This Encounter
Phase Spiders are dangerous hit-and-run predators that phase in and out of the Ethereal Plane, making them unpredictable opponents. Use their Ethereal Jaunt ability to create tension—they disappear, reappear in unexpected locations, and strike before vanishing again. Warn players with skill checks or environmental clues when the spider phases. Remember the spider can only stay on the Material Plane for 1 minute per turn, so combat naturally pulses between phases.
Combat Tactics
The Phase Spider uses Ethereal Jaunt to maximize hit-and-run attacks, appearing behind or beside targets for its venomous bite. It prioritizes isolated party members and weaker targets, phasing out after dealing damage to avoid retaliation. If heavily damaged, it may remain phased longer or flee entirely to the Ethereal Plane.
Environment & Setting
Phase Spiders thrive in web-filled caverns, abandoned structures, or planar-touched ruins where the boundary between planes feels thin. Encounter them in ethereal-attuned locations like ancient temples, fey-touched forests, or underground lairs near planar rifts.