Hints and Tips on defeating Demons/Golems/Flayers

Welp, I've tried soloing with a mage and the staff of magi staff (yes it's dirty but who cares? ) and am in Chapter 5ish in UD. However, since most things there are resistant to magic (there goes my Deathfog), I was wondering if someone else who solo'd could shed some wisdom? Especially the flayers. I've already hit the cap so any/all combos from spell lvl 1-8 appreciated

Well I know my favorite priest spell is Holy smite (I know It`s mispelled). I have a lv 13 priest of Helm going on lv 14 and I crush most enemies in a flash. I can`t wait to get Holy word!

Unfortunately, Illithid are immune to all forms of fire, cold, electricity and acid, and are 90% resistant to magic, which means you would have one hell of a battle on your hands. They're going to knock back every spell you can throw at them nine times out of ten, and once they start brain-devouring you, it's game over. Fortunately, however, you'll have a spell in your repetoire called Invisible Stalker, which is immune to both psionic charm AND brain-devour. See how that works out.

I must be lucky (just started the underdark) But I met one of the Illithids while turning the pages of a book in the asylum and 2 of my Holy Smite got through.