Magar of the Magic Strings, Sundial of the Infinite, and Warrior's Oath

Prerequisites

• Magar of the Magic Strings on the battlefield
• Sundial of the Infinite on the battlefield
• Warrior's Oath in hand
• plus each subsequent turn available

Steps

1. Cast Warrior's Oath by paying its mana cost, causing you to take an extra turn after this one and to lose the game at the beginning of that turn's end step
2. Activate Magar by paying , noting Warrior's Oath and putting it face down on the battlefield as a 3/3 creature
3. During your next turn, deal combat damage to an opponent using the face down creature that has Warrior's Oath noted
4. The creature triggers, casting a copy of Warrior's Oath without paying its mana cost
5. Resolve the copy, causing you to take an extra turn after this one and to lose the game at the beginning of that turn's end step
6. Activate Sundial of the Infinite by paying and tapping it, causing you to end the turn
7. This will prevent the Warrior's Oath trigger from causing you to lose the game
8. Repeat from step 3

Results

• Infinite turns