Originally Posted by
Ashnazg
Are you playing Vanilla BG2 (or BG2 + TOB) or modded with player-made mods? There is one called Ascension that incorporates vastly improved AI scripts for spellcasters and certain other changes to NPCs that actually make them a challenge. Not all - most of the run-of-the-mill encounters will still be cake for a properly balanced party, but they do improve quite a number of encounters (the Inn group in Amn, all of the side areas in Amn, etc). Spellcasters (as well as Dragons, and any other "boss" type mobs) pre-buff themselves, meaning you can't gib them from the get-go with 2 shots from a bow, or one backstab from an assassin. They, at the minimum, pre-buff with stoneskin, blur, and a few other goodies. Advanced spellcasters pre-buff with protections, immunities, mantle, etc.
For the summons - if you have scrolls, I believe scroll summons are insta-cast, so you can use those when you enter a new area and need meat up in a jiffy.