Imagine you are playing a Magic the Gathering game of Sealed Oath of the Gatewatch. This means your deck consists of at least 40 cards, collected from four "Oath of the Gatewatch" booster packs, two "Battle for Zendikar" booster packs, and any number of the five traditional Basic Lands. You may assume your packs contain whatever cards you want, as long as each pack has the proper distribution (1 rare or mythic rare, 3 uncommons, 10 commons, 1 land, and possibly a foil of any card in the set replacing a common). You can find a simulation here.
It is the start of a match and your opponent mulligans to 0 with a deck consisting of 40 Basic Mountains. You may not assume the outcome of any choice they make. Whenever your deck is shuffled, including at the start of the game, you may assume it is stacked in any order you like, and you may choose to play or draw. What is the fastest that you can win such a game?
Measuring the quality of a solution:
Faster is better, so winning turn 4 on the play is better than winning turn 4 on the draw, and winning in your turn 4 upkeep on the play (Hedron Alignment?) is better than winning during your turn 4 combat step on the play. For equally fast solutions, the one that deals more damage (or life loss) wins. If you're tied on both speed and damage, the winner is the one with the most style points, subjectively assigned by me.
Update: @JonTheMon's Turn 2 answer was the one I came up with when solving this myself, but I'll leave the question open for the rest of the day in case anybody comes up with something better.