Silas Renn, Seeker Adept + Ugin's Nexus + Isochron Scepter + Pull from Eternity + Umbral Collar Zealot

Silas Renn, Seeker Adept

Ugin's Nexus

Isochron Scepter

Pull from Eternity

Umbral Collar Zealot

How it works

1. Activate Umbral Collar Zealot by sacrificing Ugin's Nexus
2. When Ugin's Nexus is sacrificed, it is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
3. Move to your next turn.
4. Activate Isochron Scepter by paying 2 and tapping it, casting a copy of Pull from Eternity without paying its mana cost.
5. Resolve Pull from Eternity, putting Ugin's Nexus from exile into your graveyard.
6. Deal combat damage to an opponent using Silas Renn, triggering Silas Renn, targeting Ugin's Nexus.
7. Cast Ugin's Nexus from your graveyard by paying 5.
8. Repeat.

This loop locks in infinite turns by exploiting the replacement effect on Ugin's Nexus, which exiles it and grants an extra turn whenever it would hit the graveyard. To break that exile restriction, you use Isochron Scepter to repeatedly cast a copy of Pull from Eternity, fishing Ugin's Nexus right back out of exile and into your graveyard. From there, Silas Renn, Seeker Adept steps in as your recurring engine, letting you recast the artifact straight from the graveyard using combat damage, while Umbral Collar Zealot provides the initial sacrifice outlet to get the whole cycle rolling.