Athreos, Shroud-Veiled + Ugin's Nexus + Xenic Poltergeist + Master Transmuter + Krark-Clan Ironworks

Athreos, Shroud-Veiled

Ugin's Nexus

Xenic Poltergeist

Master Transmuter

Krark-Clan Ironworks

How it works

1. Activate Xenic Poltergeist by tapping it, 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 Krark-Clan Ironworks 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.

This intricate loop begins by using Xenic Poltergeist to animate Ugin's Nexus into an artifact creature, allowing Athreos, Shroud-Veiled to place a coin counter on it during your end step. Once Ugin's Nexus is sacrificed to Krark-Clan Ironworks for mana, its replacement effect exiles it instead of letting it hit the graveyard—triggering both its own extra turn reward and Athreos's ability to return it straight to the battlefield. From there, Master Transmuter can cleanly bounce the artifact back to your hand so you can recast it for five mana on the subsequent extra turn generated by the nexus, letting you repeat the process indefinitely.