Athreos, Shroud-Veiled + Ugin's Nexus + Karn, the Great Creator + Master Transmuter + Krark-Clan Ironworks

Athreos, Shroud-Veiled

Ugin's Nexus

Karn, the Great Creator

Master Transmuter

Krark-Clan Ironworks

How it works

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. 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 ingenious loop turns Ugin's Nexus into an endless engine for infinite turns by constantly recycling it out of the graveyard, exile, and hand. Karn, the Great Creator plays a vital role by turning Ugin's Nexus into a creature, allowing Athreos, Shroud-Veiled to place a coin counter on it during your end step so that its death will trigger a return to the battlefield. From there, Krark-Clan Ironworks provides the necessary sacrifice outlet to send Ugin's Nexus away and trigger its extra turn clause, while Master Transmuter offers an alternative path to bounce the artifact right back to your hand if you prefer to recast it.