Kaya the Inexorable, Ugin's Nexus, Karn, the Great Creator, and Altar of Dementia

Prerequisites

• Kaya the Inexorable on the battlefield
• Ugin's Nexus on the battlefield
• Karn, the Great Creator on the battlefield
• Altar of Dementia on the battlefield
• each extra turn available

Steps

1. Activate Karn's first loyalty ability by putting a loyalty counter on it, causing Ugin's Nexus to become an artifact creature until end of turn
2. Activate Kaya's first loyalty ability by putting a loyalty counter on it, putting a ghostform counter on Ugin's Nexus
3. Activate Altar of Dementia by sacrificing Ugin's Nexus
4. Ugin's Nexus is exiled instead of being put into your graveyard, causing you to take an extra turn after this one
5. Ugin's Nexus triggers, returning itself from exile to your hand, and creating a 1/1 Spirit creature token
6. Resolve the Altar of Dementia ability from step 3, causing target player to mill cards equal to Ugin's Nexus' power
7. Move to your next turn
8. Cast Ugin's Nexus by paying
9. Repeat

Results

• Infinite turns