Ugin's Nexus + Isochron Scepter + Vision Charm + Mechanized Production

Ugin's Nexus

Isochron Scepter

Vision Charm

Mechanized Production

How it works

1. At the beginning of your upkeep, Mechanized Production triggers, creating a token copy of Ugin's Nexus.
2. Put the Ugin's Nexus token into your graveyard due to the legend rule.
3. The Ugin's Nexus token is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
4. Activate Isochron Scepter by paying 2 and tapping it, casting a copy of Vision Charm without paying its mana cost.
5. Resolve the copy of Vision Charm, causing Ugin's Nexus to phase out until your next untap step.
6. Move to your next turn, causing Ugin's Nexus to phase in during your untap step.
7. Repeat.

By enchanting Ugin's Nexus with Mechanized Production, you set up a ticking clock that normally tries to win the game, but here it instead floods the board with legendary artifact copies that immediately trigger the legend rule. Because sending that token copy to the graveyard triggers Ugin's Nexus's replacement effect to exile it instead, you are granted an extra turn without suffering its downside thanks to the clever intervention of Isochron Scepter. By casting Vision Charm with the Scepter, you can phase out the original Ugin's Nexus before the legendary copy forces you to choose, allowing it to phase back in safely on your next untap step so the loop can begin anew.