a bit after this it seems that ducking when the flies and then waiting for the dive bomb to miss is the way to go as far as I can tell, but any additional advice would be tops
In the game i don't know any Achievement like "No hit run". Game has Ach like "Kill goddess on 1 lvl or Without losing you an*l virginity ".
The easiest way to "No hit run" its just pick thief and keep stealth at maximum.. Just avoid any creatures... But that boring and you still have to kill main boss...
But keep going. Your personal "Challenge" is cool.