Phase Spider

Source: Monster Manual (2024) p. 239, FRHoF. Available in the SRD and the Free Rules (2024)

Phase Spider

Plane-Shifting Arachnid Ambusher

• Habitat. Desert, Forest, Grassland, Hill, Planar (Ethereal Plane), Underdark, Urban
• Treasure. Any

Phase spiders appear out of nowhere to attack, then vanish just as swiftly. These horse-size, magical arachnids are endemic to the Ethereal Plane. From vaporous lairs, they peer through the Border Ethereal into the Material Plane. When they detect prey, phase spiders draw close and then shift or “phase” to the Material Plane to attack. They shift between planes of existence and attack from unexpected directions until they overcome their prey or are forced to retreat.

Phase spiders are more intelligent than mundane spiders, but most are cowards. They usually flee if they’re outnumbered by creatures capable of seeing them on the Ethereal Plane or pursuing them there. They make exceptions for ghosts and similar spirits, which phase spiders gain sustenance from and pursue as favored prey.

A quote from Marcus Wands, Doubtful Authority

Some sages say you unknowingly occupy the same ethereally coterminous point as a phase spider an average of four times each year.