Otyugh - the wonderfully nasty cross between Beholders, Pak'ma'ra and Illithid. Disease is a mechanic that has lost favor in current editions due to forcing the DM/GM to have to remember specific events in the game. However, I'm leaning more and more towards just marking down when a PC has the chance to be diseased and not saying anything, then asking that player to roll the save at the end of the night. Often they have forgotten about whatever might have happened to cause said requested die role. This prevents them from immediately knowing to get a cure disease spell and heightens the mystery of what is happening.
Yeah, so disease, that's great, what else makes them interesting? Well, for one, they are large with long reach (longer than PCs with long weapons if you are using minis). If you aren't, then the players have to say they are getting close enough to attack, which should give you ample opportunity to attack, trip, grapple them.
The other thing I love about Otyugh's is that they often have deals worked out with more intelligent beings in the area. Meaning that if the PCs kill an Otyugh, they've probably pissed-off the locals. So? Well, the locals are probably going to notice when their trash isn't being taken care of when they expect it to. So if you have PCs trying to sneak through an area, they may have inadvertently given away their presence. If they aren't trying to sneak through that Drow/Druegar/Illithid controlled zone, the Otyugh probably has a deal worked out to let their "employers" know that intruders are in the area.
Yeah, that's not really a battle tactic. Sure it is, cause why would an intelligent monster straight up attack an armed invading force. They don't, they go tell those who's job it is to get rid of the intruders, then it's time for the buffet.
Ok, so here's something to think about. The party is probably going to search out a defeated monsters lair, well, that's GREAT. What's in an Otyugh's lair, DISEASE, rats (possibly dire size), spiders (possibly large), DISEASE, some coin, maybe a potion or two, DISEASE, a couple of gems, a minor magic item, DISEASE, a mate or offspring or two, possibly some traps and the fact that if the party spends any time in the lair, they are going to smell of carrion - always pleasant when trying to negotiate passage through neutral or hostile terrain.