When you meet with farah after the brothel,there will a cutscene in which mahasti will throw an axe at you. Climb up to the save fountain and then a platform in which mahasti will be waiting for you.use whatever fightinig tatics you prefer.if you get knok of the platform then rewind time.after a while you will turn in dark prince. When you get to the platform shes on slow down time or she will run away.Keep on doing that and youll enter a deadlock and press x fat as you cab abd you win.Also kill enemys on the platforms and use their sand to replenish your heatlh when your playing as dark prince.