Carth the Lion, Karn, the Great Creator, Ugin's Nexus, and Throne of Geth

Prerequisites

• Carth the Lion on the battlefield
• Karn, the Great Creator on the battlefield
• Ugin's Nexus on the battlefield
• Throne of Geth on the battlefield
• each extra turn available

Steps

1. Activate Throne of Geth by tapping it and sacrificing Ugin's Nexus
2. Ugin's Nexus is exiled instead of being put into your graveyard, causing you to take an extra turn after this one
3. Resolve the Throne of Geth ability, putting a loyalty counter on Karn
4. Activate Karn's second loyalty ability by removing a loyalty counter from it, returning Ugin's Nexus from exile to your hand
5. Move to your next turn
6. Cast Ugin's Nexus by paying
7. Repeat

Results

• Infinite turns