Eye of the Beholder by SSI!
The second in the trilogy was my favorite. The skeletal knights were the scariest part of the whole adventure. They were nearly indestructible and hit hard. The only way to win the encounter was to hit-and-retreat at just the right pace so that they would miss most of the time. And they were smart enough to try and split up and flank your party around corners. If you retreated into an open room you were toast.
