"Not sure if it is due to the tactics mod but I was in the Drow city, fighting the Lich, Deriex or something, and he casted a Mordi Sword at me. Now I had my mages hit it with magic missiles and minute meteors. Both were not doing any damage. Any one came across this ?"
you can only attack it with magic damage. all other res are up to 100% which means immunity (lower res works
). i think magic missile damages the sword, too, because it does magic damage.
"I have noticed the Liches now behave differently than the last time I played. They teleport me party in every now and then. They also dispell a lot."
this is due to tactics which improves all mage scripts.