Had a couple thoughts on battle magic from the whole Supreme Patriarch duel discussions.
First, when using invisibility casting battle magic would reveal us. We can act and cast when invisible iirc, back during our Magister exams there were thrown shadow knives while invisible, but the movement of said Ulgu revealed the caster.
Invisibility works because it makes things invisible, because magic. This also applies on the magic inside us, otherwise it would be pretty useless on Windsight, not to mention potentially seeing the magic of the invisibility spell itself. However, disturbances in the ambient Ulgu (and other Winds) are still noticeable, which I imagine would be extremely obvious to any Wizard Lord when their invisible opponent starts channeling the necessary Winds for battle magic.
Could we then create a spell to make all of the Ulgu in an area invisible to others, using this property of invisibility and Warrior of Fog?
This would mean people wouldn't be able to sense us even while invisible and casting battle magic, nor what we're doing with our magic until it's already cast and reality is screaming. Could even interfere with enemy casting efforts if they also use Ulgu; I imagine it's a lot harder to fumble through a spell if you can't see what the magic is doing.
Could try extending the effect beyond Ulgu if the magic interference effect is potent enough, though that's probably too ambitious.
Wouldn't be a very good true stealth spell; any decent enemy caster would notice all that magical energy vanishing from their senses. Malfean stealth is fun too though.