he could say "DIE" then accel could die but as for the method their are ways to avoid it or countering it.
Aureoulus alchemy isn't perfect. It couldn't go further than what he could thought or think and beyond that is impossible. That's why he needs to be calm all the time because if his mind go astray then the magic would be dispel.
As for methods he could say that to suffocate but then accel would use other ways to breath and if Aureoulus would say explode then Accel would just counter it.
It depends on the spell cast. Accel can and canoot counter it. Plus if Accel did meet face to face with Aureoulus. I think Aureoulus would instantly loose its mind
That guy is a psycho >< and the requirement for his ars magna is a complete calm mind and small disturbance would cause instability on the magic.
So that's why I said if Accel and Aureolus would fight and accel enter the ars magna realm but can't see aureolus the chances of him winning is huge but if accel did meet aureoulus then the chances of accel winning is huge.