The Gargantuan Spider
I'm by no means an arachnaphobe, and yet this creature always seems to find itself into one of my campaigns. It is one of my favorite boss monsters, because there are so many types. One of my most memorable encounters using this monster, involved the aquatic Diving Bell Spider. For years I've been running a pirate campaign where water is the main theme. It has been an excellent opportunity to use all those aquatic monsters that would otherwise not see that much use. The spider is perhaps the most generic monster in D&D, and yet there are so many interesting variations of it!
The players found themselves in a large cave with a round stone platform in the middle. On this platform was a mysterious stone coffin, sealed with evil magic. A partially collapsed stone bridge was the only means of reaching the central platform. Down below, the cave was filled with water. Little did the players know that below the surface of the water was a vast underwater spider nest made from webbing. Countless remains of previous adventurers, along with their gear, were wrapped into grizzly little cocoons of pure nightmare fuel. But where were the spiders...?
Along the steep cave walls were three waterfalls, and the spiders were waiting in caves behind them, hidden from sight. As the players approached the platform they would fling their webs through the water and at the players. If they landed a hit, they would attempt to pull the players off the platform and into the web-filled waters below.
As the spiders sprung their deadly ambush on the players, the much larger Queen spider slowly descended from the ceiling onto the platform...