Can you take flaws for extra feats at 1st level?
If so, human Sorceror 1/Rainbow Servant 10/Sacred Exorcist 1/Geomancer 4 (the latter "just because")
If no flaws, human Sorceror 4/Rainbow Servant 10/Sacred Exorcist 1/Something-Advancing-Spellcasting 1
You have 16th-level Sorceror casting, which will include Wings of Cover for immediate-action "everything" avoidance. You can spontaneously cast
any cleric spell of up to 8th level. You have turning attempts and - because you cast cleric spells that are not also on the sorceror/wizard list
as divine spells - you also have divine metamagic shenanigans. You can also fly as a
supernatural ability, which means it isn't subject to being dispelled.
This build relies on your DM playing by the RAW "text trumps table" rules though, otherwise Rainbow Servant isn't worth it. Oh yeah, and they've got to be amenable to at least some (ahem) mild early qualification shenanigans via Versatile Spellcaster *.
In which case, play a Psion. With a Psicrystal. Using Metamorphosis and Metamorphic Transfer, you have your Psicrystal train his Beholder antimagic beam on the players you aren't currently pounding - to keep (at least one of) them in line - whilst you use your Choker quickness to explodify someone else twice per round. Or, you know, just use Amethyst Burst a lot. If you can give your Psicrystal access to White Raven Tactics, so much the better. Damp Power will be very useful if you're facing other psions or damage-dealing spellcasters.
Be sure to break the action economy into
very tiny bits, and don't forget to stomp on those bits when you're done
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* The first build, of course, relies on utterly outrageous early qualification abuse via Versatile Spellcaster, Heighten Spell, Earth Sense and Earth Spell. Horrible, I know, but if you don't ask you don't get