Thanks for all these answers
I can handle mages who use improved invisibility; with dispell invisibility, true sight and wands followed by various spells to strip the magic from the mage (pierce, warding whip etc)
I still have problems with level 15+ mages. They use spells like mislead and sanctuary, or go ethereal. This means you can't target them with any of your own spells. Area effect spells tend to be relatively ineffective - they either have protection or they save vs spell.
Attacking the mage before they get their protections up is a very good idea. Higher level mages will have contingency and spell sequencers that take place almost immediately, but these protections are lower in level than the ones that take more time. A good backstab can do wonders, as can some seriously nasty missiles.
Playing mods is so much fun, but you do run across more difficult situations - where the mages are
much higher in level or they come in groups. Like Tricky the only strategy I've found is to wait for the spells to wear off , and to use up their replacements while doing everything I can to stay alive.