Aspiring Champion and Leyline of Transformation on the battlefield (Leyline of Transformation with "Demon" chosen).
Aspiring Champion does not have summoning sickness, and cannot be blocked by an opponent.
Your life total is at least 3.
({B} magic symbol) available.
Steps
Cast Vampiric Tutor by paying ({B} magic symbol) , searching your library for Blightsteel Colossus and putting it on top of your library, then causing you to lose 2 life.
Deal combat damage to an opponent using Aspiring Champion.
Aspiring Champion triggers, causing you to sacrifice it, then reveal Blightsteel Colossus from the top of your library and put it onto the battlefield as a Demon due to Leyline of Transformation, then causing Blightsteel Colossus to give each opponent eleven poison counters.
Each opponent loses the game as a state-based action due to having ten or more poison counters.