Don't mind me, I've been playing Baldur's Gate 2.

I think mana mixing going haywire (technical term, honest) might be interesting if it works the same way as when a Wild Mage's spell goes wacky.

Some of the Wild Mage effects in BG2...

-everyone starts glowing
-money vanishes
-money appears
-target of spell becomes confused
-explosion
-cow drops from the sky onto target of spell
-spell cast twice
-caster falls asleep