To put it plainly:
Lord Neverember has heard rumblings of a wizard performing strange illusory experiments deep within the sewers of Neverwinter. Nothing bad has happened; in fact, some of the seedier elements of the city have fled due to the wizard’s strange actions. Lord Neverember has asked a group of adventurers to investigate what’s happening, knowing that the Sword Coast has a bad history of wizard’s experimenting in sewers.
According to the blog, Cryptic Studios has put great effort into ensuring that this skirmish is as fun on the twentieth playthrough as it is the first. In other words, randomness! From the layout to the formations of enemies.
Players can check out the new skirmish now on the preview shard, or wait till it goes live in Modile 11.