Assuming I get full casting, how'zbout this build?
TN Whisper Gnome Beguiler1/Rainbow Servant10/Shadowcraft Mage5/Mindbender1/Full Casting3
I use early entry tricks to reach Rainbow Servant @2. I take all 10 levels due to needing an Illusion (Shadow) spell of level 4 or higher, which Clerics get. (A Heightened
dark way qualifies, as does a plain ol'
skull of secrets spell.) Shadowcraft Mage5 is just because, well, Shadowcraft Mage, and provides a thematic power boost. I included Mindbender1 due to it just rocking.
I'm tempted to say "Include Archmage in this build!" because it sounds cool and it didn't originally seem possible, but its 2 additional feat prereq turns me off. (Those feats could instead be used on Shadowcraft Mage goodiness!)
Rearranging things and going Mage of the Arcane Order doesn't seem worth it due to it costing 2 additional feats (Arcane Preparation and Cooperative Spell) OR one additional level 1-only feat,
Magical Training. (Magical Training also requires your GM being OK with using this feat for entry.)
Incantatrix is a very tempting inclusion for this build, for it is effectively the best general arcane casting PrC there is in 3.5. Mystic Theurge is possible but cheesy due to Rainbow Servant10 granting access to the entire Cleric spell list... as Divine spells known... on the same class list (Beguiler) that also casts arcane spells. What else do you suggest?