The Sixth Doctor, Karn's Temporal Sundering, Isochron Scepter, and Unsubstantiate

Prerequisites

• The Sixth Doctor on the battlefield
• Karn's Temporal Sundering in hand
• Isochron Scepter on the battlefield
• Unsubstantiate in exile
• each turn available

Steps

1. Cast Karn's Temporal Sundering by paying
2. The Sixth Doctor triggers, copying Karn's Temporal Sundering
3. Resolve the copy of Karn's Temporal Sundering, causing you to take an extra turn after this one
4. Holding priority, activate Isochron Scepter by paying and tapping it, casting a copy of Unsubstantiate without paying its mana cost
5. Resolve Unsubstantiate, returning the original Karn's Temporal Sundering to your hand
6. Repeat each turn

Results

• Infinite turns