Athreos, Shroud-Veiled + Ugin's Nexus + Xenic Poltergeist + Master Transmuter + Ashnod's Altar

Athreos, Shroud-Veiled

Ugin's Nexus

Xenic Poltergeist

Master Transmuter

Ashnod's Altar

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 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.

This intricate loop bends time to your will by continuously recycling a single artifact for endless extra turns. First, Xenic Poltergeist temporarily turns Ugin's Nexus into an artifact creature, allowing Athreos, Shroud-Veiled to place a coin counter on it during your end step. When you sacrifice that same Ugin's Nexus to Ashnod's Altar for mana, its replacement effect exiles it to grant you an extra turn while simultaneously triggering Athreos, Shroud-Veiled to return it straight to the battlefield. To reset the engine for the next cycle, Master Transmuter bounces Ugin's Nexus back to your hand so you can recast it on your newly granted turn.