Sounds like you need to vet your players better. That Krucian sounds either highly cheesed or illegal. And just because something is in a book doesn't mean you have to allow it.

As for defeating high AC... an intelligently played batman/god wizard has no issues with crazy AC. Also look at the various summoning/minion classes like malconvoker, dread necro, uttercold assault necro wizard etc.

Failing that, higher CR monsters, monsters with character levels (suitably optimized of course), armies of mooks with touch/splash weapons (several dozen kobolds with flasks of acid/oil + torches).