Carth the Lion, Karn, the Great Creator, Ugin's Nexus, The Chain Veil, and Phyrexian Altar

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
• Phyrexian Altar on the battlefield
• on your first turn, with available on all subsequent turns available

Steps

1. Activate Karn's first loyalty ability by putting two loyalty counters on it, causing Ugin's Nexus to become an artifact creature until end of turn
2. Activate Phyrexian Altar by exiling Ugin's Nexus, adding
3. Ugin's Nexus triggers, causing you to take an extra turn after this one
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. Repeat

Results

• Infinite turns