In a Two-Headed Giant game, each team with 13 life loses the game, then each player on each team gains or loses 1 life, causing the team’s life total to go up or down by 2.

If each player has 13 life as Triskaidekaphobia’s ability resolves, the game ends in a draw.

You choose one of the modes even if no player will lose the game. Players will still gain or lose life as appropriate.

If you choose Triskaidekaphobia’s second mode and begin to resolve it while an opponent’s life total is 13 and your life total is 1, that opponent will lose the game before you lose 1 life.