Requires

Osgir, the Reconstructor must be on the battlefield. Karn, the Great Creator must be on the battlefield. Ugin's Nexus must be in the graveyard. Birgi, God of Storytelling // Harnfel, Horn of Bounty must be on the battlefield (on the battlefield as Harnfel, Horn of Bounty). Anointed Procession must be on the battlefield. Mana needed: available, with an additional every fourth turn

Steps

1. Activate Osgir by paying , tapping it and exiling Ugin's Nexus from your graveyard, creating four token copies of Ugin's Nexus.
2. Put three of the Ugin's Nexus tokens into exile due to the legend rule and their replacement effects, causing you to take three extra turns after this one.
3. Activate Karn's first loyalty ability by putting a loyalty counter on it, choosing to do nothing.
4. Move to your next extra turn.
5. Repeat from step 3 one additional time.
6. Activate Karn's second loyalty ability by removing two loyalty counters from it, returning Ugin's Nexus from exile to your hand.
7. Activate Harnfel by discarding Ugin's Nexus.
8. Move to your last extra turn.
9. Repeat.

Results