Normal MtG rules apply here. Your solution must work regardless of any possible choices made by your opponents; assume they do whatever makes it most difficult for you to win. If you would draw a card, you may assume that you draw any card remaining in your library, regardless of shuffling.
You are playing in a multiplayer game of Magic. Decks are 60+ cards, no ban list besides unglued/unhinged, maximum four of each card unless the card says otherwise (or is a basic land).
All the other players have been eliminated, leaving only you and one opponent. It is your opponent's first main phase, nothing has summoning sickness, and no spells have been cast yet on his turn.
Win the game!
(If there are multiple solutions, the best is the one which wins on the earliest turn, secondary tiebreaker is dealing the most damage)
Whatever you want