Athreos, Shroud-Veiled + Ugin's Nexus + Karn, Silver Golem + Master Transmuter + Ashnod's Altar

Athreos, Shroud-Veiled

Ugin's Nexus

Karn, Silver Golem

Master Transmuter

Ashnod's Altar

How it works

1. Activate Karn by paying 1, causing Ugin's Nexus to become an artifact creature until end of turn.
2. At the beginning of your end step, Athreos' second ability triggers, putting a coin counter on Ugin's Nexus.
3. Activate Ashnod's Altar by sacrificing Ugin's Nexus, adding CC.
4. Ugin's Nexus is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
5. Athreos' third ability triggers, causing you to return Ugin's Nexus from exile to the battlefield.
6. Activate Master Transmuter by paying , tapping it and returning Ugin's Nexus to your hand, choosing to not put an artifact onto the battlefield.
7. Move to your extra turn.
8. Cast Ugin's Nexus by paying 5.
9. Repeat.