The Tainted Spiral

From the publisher's website and first page of the module - The Tainted Spiral is a short adventure for five 1st‑level characters that takes place in the Chaos Scar. The adventure is set in a spiraling network of tunnels carved a by a piece of the great meteor, called a Chaos Shard, that broke away when the comet crashed to the earth. Like the meteorite itself, the Chaos Shard is a malevolent force of chaos and evil that draws other evil creatures to it. The presence of the Chaos Shard has weakened the barrier between the world and the Far Realm, creating rifts in reality that have allowed a number of fell taints and other terrible aberrations to heed the shard’s call