Thunderspire Labyrinth must have been getting sick of Duergar (I know I was) because suddenly we get a Ruined Chapel full of wights.
This is the Horned Hold's "secret passageway". Once players have reached the western guard post, they can choose to come here via a neglected and disused corridor as an alternative to fighting through orcs, ogres, and a very grumpy paladin of Asmodeus.
The Duergar apparently avoid this area because they're too lazy to clear out the undead that infest it. The undead in question are wights, described here as "long dead human warriors in tattered black mail".
This, of course, doesn't make a lick of sense. In case we've somehow forgotten, the Horned Hold used to be a minotaur fortress. More recently, it's been run by Duergar. How armed undead humans managed to make their way to this single room of the complex is a mystery mortal minds were not meant to solve. The obvious improvement is to make the creatures here either Duergar wights (meh) or minotaur wights (highly awesome).
Players of previous editions know wights as monsters to avoid. That's because of their energy drain, also known as "level drain". That is to say, by merely touching you they could strip you of a character level. Recovering that level by any means other than re-acquiring the XP called for one of several medium to high level cleric spells. Those are spells, naturally, that PCs don't get until many levels later.
The level drain was scary. It was a longstanding tradition. It was one of the memorable things about fighting undead.
But, importantly, it was bollocks. Losing things is not fun. We hate it. In fact, we hate it disproportionately.
In 1980 a man named Robert Thaler noted that, contrary to standard economic theory, people seemed to place a higher value on items that they own than an equivalent item that they didn't. That is to say, people would ask for more money to sell an item that they currently had than they would pay to buy an identical item. He called this the "endowment effect".
In 1990, Tversky and Kahneman went on to demonstrate this as a result of a specific form of cognitive bias called loss aversion. Humans, they argued, are essentially averse to loss. We find losses more distressing than equivalent failures to gain. We are much happier about missing the opportunity to gain $100 than we are about losing $100 we thought we had.
What does this mean for game design? It means that taking things away from players is a big stick. It is a disproportionately big stick. It means that people will make bad decisions when a loss is a possible consequence. It means that people will get irrationally upset when a feature or resource of their character is deleted.
You only need to look at the forums to see this. People hate having their favourite class nerfed. They're not nearly so worried about missing out on being buffed, though. People scream loudly about cancelled D&D Insider features they thought they were getting; they're not quite so vociferous in requesting additional features that haven't already been offered.
D&D 4th Edition has taken loss aversion to heart. Classic "progress eating" game mechanics have been dramatically changed. The Rust Monster, for example, no longer deprives players of thousands of gold worth of magical items without offering commensurate reward. Enemies with "weaken" powers no longer lower stats, and being raised from the dead won't permanently erase a point of Constitution.
And the wight, our feature monster here, doesn't drain levels. He instead knocks off his victim's healing surges. A horrifying permanent loss has been replaced by a temporary elimination of the PC's ability to regain hit points.
It's an improvement. I can tell you, I am absolutely never going to miss having one of my levels drained. That is an experience I am overjoyed to see in the past.
But at the same time, I kind of miss knowing that there were things out there that could steal levels. How are DMs going to terrify low level players now?