Every adventure or story needs a good premise, and one way to get that premise is from a great villain.
Post your villain ideas here.
Medusas - A classic monster dating back to Greek Myths. In every story about a Medusa, there is always a statue garden.
A Medusa Sorceress has claimed a demesnes near Stormreach and, under the effects of a disguise self spell, has been luring people from the city to add to her collection. Recently, she has drawn the young nephew of one of the Coin Lords away and he now stands petrified in her garden.
Warforged and Dryad - Warforged are made from Stone, Metal, and Livewood. Livewood continues to live after being cut. Some Dryad in Eberron are bonded to livewood trees and they survive their tree being cut, and even shaped. Some Dryad are now bonded to airships or thrones. Perhaps one is bonded into the construction of a warforged.
Or, tie Haywire back in.
Haywire just can't get over his obsession with warforged. His most recent experiment involved cutting down and shaping a Dryad's livewood tree for use in one of his drones. Haywire hoped that the Dryad would infuse this drone with true consciousness. It didn't work, and now the drone--under the Dryad's control--is out for revenge and with her new mobility, Haywire can't just run away.
House Tarkanan - While not a true Dragonmarked House, those claiming to be of House Tarkanan are bearers of the Aberrant Dragonmark.
Representatives of house Tarkanan have come to Stormreach and are taking members of the Quickfoot prisoner in a bid for power. Among the captured was an Sentinel Marshal of House Deneith that infiltrated the criminal organization. House Deneith wants their investigator returned safely, but the Coin Lords won't allow them to call upon the Defenders or Blademarks.
Cult of the Dragon Below (Possibly a chain) - A Daelkyr Prince is trying to force its way into Eberron. So far he has managed to push a number of his minions through the barriers to the world and established a growing cult. His progress is slow because he doesn't want to share Eberron with the other Princes of Xoriat.
Living Spells - A nominally talent wizard has gone insane in her pursuit of power. Using unstable materials to augment her spells, she has tragically created a horde of living spells. Now Living Burning Hands, Living Webs, and other animated spells threaten to spill out onto the streets.
Followers of the Broken Path and Lord of Blades - Representatives from the warforged druidic order have come to Xen'drik hoping to find knowledge to help them in their quest to heal the Mournland. Unfortunately warforged loyal to the Lord of Blades have followed them here to stop them to kept the Mournland "the perfect homeland for warforged."
That's all I can think of, anyone else have ideas?