Complex sentence: Cole tries to give up the Source to the Wizard after his human side becomes strong and Phoebe learns through a premonition that he is a demon again but before the ritual is complete, the Seer who has manipulated Phoebe interrupts and vanquishes the Wizard.
Split into simpler sentences: Cole tries to give up the Source to the Wizard after his human side becomes strong and Phoebe learns through a premonition that he is a demon again. But before the ritual is complete, the Seer, who has manipulated Phoebe, interrupts and vanquishes the Wizard.