I don´t like to use that sort of tactics, but when I went the second time through mind flyers dungeon, I didn´t want to do all this hard stuff again, so here it is, although probably known by the most:
Just take some invisble guy, put him in the doorway, enemies won´t be able to pass him, neither they see and attack him. Now take out the crowd gathering behind your invisble player just with your distance weapons. Grat for annoying life-sucking vampires.
Especially for mindflyers: Let one charackter stay close behind the invisble, so they make their mindscrewing blasts on this one. Cheap, but helps.
st.Schnupps