Cast Saw in Half by paying ({2} magic symbol) ({B} magic symbol) , destroying Returned Pastcaller and creating two token copies of it with base power equal to half the destroyed creature's power and base toughness equal to half the destroyed creature's toughness, rounding up each time.
When the Returned Pastcaller tokens enter the battlefield, they trigger, returning Saw in Half and Cabal Ritual from your graveyard to your hand.