You are mixing up requirements for becoming a Magister Lord, and spending favour to learn a Battle Spell as a Magister.
Former requires pretty specific traits due to being not merely strongest, baddest mages of the Empire but ideological and political leadership of the Colleges of Magic. The latter could be done by having a bunch of "general" rep points and spending a lot of favour points. It is, in truth, not too much different from spending a bunch of favours to get Seed of Regrowth. Only significantly more expensive.
Considering what kind of options Dorf rep at 20-ish and Dorf favour at "Unknown, but significantly higher" did for us, I suppose that somewhere in between that range option to spend favour to learn a single Battle Magic spell would become available without college pressing us into becoming a Battle Mage.
Went and found the QM posts in question:
A Magister with sufficient seniority, a proven track record with the most difficult sub-Battle spells, an impeccable reputation, and some College Rep to spend might be able to swing a spell or two.
Very good, but your Magister rank is brand-new. Your joining the Expedition is not a point against you, but would lead some to think you still need to get some youthful exuberance out of your system.
So while MagisterLord is much more difficult, even getting a "might be able to" for battle magic is difficult; we have the track record with spells, and a good reputation, but we have almost no seniority, and that good reputation is more in terms of 'skilled' than 'proven and seasoned', which as i understand it is the type of reputation we'd need.
If we are doing Battle Magic at all, I'd say that Teleport signature spell that will allow us to blink with every Fiendishly Complex spell cast is where it's at for Mathilde. Should be less expensive in terms of favor compared to the Big Flashy Nukes and actually slots nicely into her current kit and preferred modus operandi far better when compared to flashy stuff like Pit of Shadows.
Boney has actually straight up nixed the idea that it might be less expensive, because:
No. Battle Magic is Battle Magic.
As for the general 'can we cast teleports without miscast chance', the book of spells description is ambiguous as to whether "cast alongside fiendishly complex spells without additional miscast chance" means "normal FC chances and nothing else" or "normal FC chances for the FC, normal Battle magic chances for the teleport, no additional complexity from combining", but given this:
1. It would depend on how prominent Ulgu was at the time, how difficult that specific spell was, how long and how well you can concentrate, and whether there's any enemy wizards around to interfere. You'd be lucky to get coinflip odds.
And the 'battle magic is battle magic' quote, i personally would assume its the latter--specifically with the 'how difficult that specific spell was' being among the lowest DCs for battle magic, but still subject to the 'lucky to get coinflip odds at current skill', especially if we're using it in combat to escape.
Of course, the real solution here is to just ask
@BoneyM to clarify how exactly the miscast chances and 'fit in with other spells' stuff works for it
Quick edit: that said, i do agree that if we go for battle magic, Smoke and Mirrors or Steed of Shadows for 'get the fuck out of dodge' and 'battle maneuvering' options would be my votes. Just personally i'd prefer we focus on 1. completing the standard spell book and then 2. creating Warrior of Fog (or any future spell traits we pick up) spells as opposed to going for battle magic,as those are less risky while still being quite powerful, and the former lets us increase our magic rating, while the latter earns us college favor instead of costing it
