Using Phyrexian mana to cast instants at little to no cost, I can pump up my kiln fiends quickly running in for 10+ damage.  With a quick fling, the game is over.

Death's shadow teamed with Immolating Souleater allows me to sacrifice my own life for a big attack and summon a cheap heavy hitter for defense or another game winning fling.

Works quick with the right cards in hand and is much better in a two player game.