First off, do you think this actually works with Coven Casting to begin with?
Cavalier/Samurai Order of the Staff wrote:
Spell Aid (Ex)
At 2nd level, whenever the cavalier uses the aid another action to assist one of his allies, the ally receives a +2 competence bonus on the next concentration check, dispel check, or caster level check she makes (whichever comes first). At 8th level and every six levels thereafter, this bonus increases by an additional +1.
Pretty sure the bonus applies to CL "checks" and not the actual CL, itself. But that's ok, I still really like the somewhat synergy.
I'm kind of thinking a Disciple of the Pike Cavalier, Order of the Staff... Caster's Champion, AWT:Abundant Tactics, Dueling Gloves, and Riving Strike... should go well with the Order of the Staff Challenge, maybe?
Might even VMC Witch, just for fun... although it is probably easier to start with a class that has access to the Coven Hex or Accursed Bloodline, and then VMC Cavalier for the Order.
Well, when it comes time to raid the highly-magically-warded castle of Count Turtle Von Goaway, that hefty Dispel Check is certainly going to come in handy.
Shaman with the Tribe Spirit, VMC Cavalier for Order of the Staff, takes the Coven Hex?
Tribe Spirit's Tribal Cooperation gives you 1 teamwork feat, VMC Cavalier gets you 2 more... Allied Spellcaster, Metamagical Synergy, and Harrying Partners...