Carth the Lion, Karn, the Great Creator, Ugin's Nexus, The Chain Veil, and Krark-Clan Ironworks

Prerequisites

• Carth the Lion on the battlefield
• Karn, the Great Creator on the battlefield
• Ugin's Nexus on the battlefield
• The Chain Veil on the battlefield
• Krark-Clan Ironworks on the battlefield
• available on all odd-numbered extra turns, with available on all even-numbered extra turns
• on your first turn available

Steps

1. Activate Krark-Clan Ironworks by exiling Ugin's Nexus, adding
2. Ugin's Nexus triggers, causing you to take an extra turn after this one
3. Activate Karn's first loyalty ability by putting two loyalty counters on it, causing any artifact to become an artifact creature until end of turn
4. Activate The Chain Veil by paying and tapping it, allowing you to activate all planeswalker abilities an extra time this turn
5. Activate Karn's second loyalty ability by removing a loyalty counter from it, returning Ugin's Nexus from exile to your hand
6. Move to your next turn
7. Cast Ugin's Nexus by paying
8. Activate Krark-Clan Ironworks by exiling Ugin's Nexus, adding
9. Ugin's Nexus triggers, causing you to take an extra turn after this one
10. Activate Karn's second loyalty ability by removing a loyalty counter from it, returning Ugin's Nexus from exile to your hand
11. Move to your next turn
12. Cast Ugin's Nexus by paying
13. Repeat

Results

• Infinite turns