It's those VAMPIRES who run around the streets at night; I never know exactly when or where I'll run into them - I'm afraid to walk the streets at night, seriously - they run so fast, our clerics have almost no time to throw up a couple of Negative Plane Protections, and Turn Undead has a delay too. Even then, usually one or two of us has to go to Level Drain Hospital. What a nightmare. Well, Bodhi's hot
but all the others are wicked.
Mind Flayers are bad, but usually they congregate in a room which you can scout beforehand with Invis or Stealth, and you can get prepared well in advance. Vampires ambush you.
Favorite "red-circle" character - Irenicus (David Warner is outstanding)
Favorite fights - probably liches, with all the casting they do, it's like a firework display, and they have a SICK dance