Batman's Bane: The Joker

[Temp.]

First off, because the Joker Bard does 99% of his stuff without magic. And Second, because of Glibness. It's Bard only, not Sorc/Wiz, so Beguilers can't get it. Being able to lie and get away with it, even under Compel Truth and Zone of Truth is absolutely critical for this build.

Good thing the Beguiler gets Glibness a level before the Bard? And can cast it more often?

Bards get just as many skills as Beguilers do, both are 6+ Int mod. How does he end up with fewer skills as a Bard?

Intelligence-based casting will usually mean more Intelligence and more skills. It's more of a PC thing, but it might matter.

I don't put much stock in Bardic Knowledge. A good social network should cover this for the Joker's purposes.

[edit:]

Again, this is a guy who can, with 10 minutes of RP and not a single spell, can change a man's morale compass so completely that he goes from Harvey Dent to Two Face. Can your beguiler even begin to match that?

Err... what? The only thing Bards have along these lines that Beguilers don't is Suggestion. And that's just a spell with a different label.