Dark Tide Rising
Entity from the dream plane
The dream entity was first encountered when the party made their second trip into Hargo’s mind. The psychic portal that the party used to enter Hargo’s mindscape the first time did not fully close for some unknown reason, so they returned to seal it. The dream entity used false images to trick the party into severing Hargo’s silver cord, permanently un-tethering his soul from his body. As soon as this was done, the entity possessed Hargo’s body, and fled Winterhold.
The party soon learned that Phargo (the group’s nickname for the dream-entity-possessed Hargo) had managed to hire a ship and crew in Avery. They teleported to the ship as it was sailing south on the Heartsea, and did battle with Phargo and its minions. They defeated the entity, but Hargo’s body and several party members were disintegrated in the process. These events were undone when the party traveled back in time to the previous day.
Phargo established a base of operations in the Pirate Isles and began summoning creatures from the nightmare realm to possess human hosts. The nearby area slowly became coterminous with the dream plane. The dream entity was well on its way to becoming a quasi-deity, when the party returned (with the help of Borg) and defeated the creature for good.