I enjoy titles which convey everything that you need to know about the topic.
So I'll probably be getting in on a game soon, starting at Level 10 (probably), wherein the GM is a bit of a nut who is wildly unconcerned with party balance.
So I decided that I'd like to bust out a character I'd once considered but thrown away as unlikely to ever be accepted by reasonable men, since he's vetted and approved it.
The PF Young Banelar.
For those of you who aren't in-the-know, the Pathfinder Monsters-as-PCs rules can be found here: http://www.d20pfsrd.com/bestiary/rules-for-monsters/monsters-as-pcs
As you can probably figure from even the briefest glance, this can make for some wildly overpowered dealings. The GM agreed to use them.
The Banelar is a creature in Monsters of Faerun that gains, at CR 5, 6th-level Wizard and Cleric casting, all their spells use only verbal components(!), they effectively gain a free Quicken Spell every round, and they have +6 Int & Wis, +10 Con, and other shinies like 7 hit dice and a couple random immunities.
But because Huge size and an odd CR are both impractical, you can throw the PF Young template at them to get them down to 4 CR and Large size. You lose some Constitution bonus, but you still have +6 and the other benefits basically outweigh this, since you're not a goddamn Hulking Hurler, you're the Alpha Male of spellcasters.
So basically a Young Banelar is King Shit with Pathfinder rules.
Now, I figure that this creature is a great opportunity to finally get some use out of the Mystic Theurge, since you can jump into it without losing any caster levels from either class. By level 10 (when my Monster ECL has been shaved down to just 2 CR) I could be at MT 8 and thus have 14th level casting in both classes. I consider this more than equitable from any optimization standpoint.
But I have two questions: first, is this still the best use of the Banelar's talents? Would focusing on one casting progression (say, Banelar 2/ Incantatrix 8) be for the best? And second, if I do go for Mystic Theurge... Well, where do I go from there? By Level 12 I'll be finished and have 8 levels to play around with. That's enough to get 20th level casting in both classes, but I wonder if any specific path stands out. (I dunno, Banelar 2/ MT 10/ Incantatrix 8?) Not to mention the fact that I haven't even thought about feats, or synergizing my standard spell loadouts, or anything like that. Aside from XP-free Wishes, I guess.
So I guess that opens the discussion. Anyone who has any thoughts at all on the matter, sound off.
EDIT: I didn't make it clear at first that the GM has agreed to use the PF Monsters-as-PCs rules and supports them, so I figured I'd clarify that he has.