Havoc Festival, and Archfiend of Despair

Prerequisites

• Havoc Festival on the battlefield
• Archfiend of Despair on the battlefield

Steps

1. At the beginning of each opponent's upkeep, Havoc Festival triggers, causing them to lose half their life total, rounded up
2. At the beginning of their end step, Archfiend of Despair triggers, causing each opponent to lose life equal to the life they lost this turn
3. The opponent whose turn it is loses the game due to having zero or less life
4. Repeat during each other opponent's turn

Results

• Each opponent loses the game
• Near-infinite lifeloss