Mechanized Production + Ugin's Nexus + Teferi's Realm

Mechanized Production

Ugin's Nexus

Teferi's Realm

How it works

1. At the beginning of your upkeep, Mechanized Production and Teferi's Realm trigger.
2. Resolve the Mechanized Production trigger, creating a token copy of Ugin's Nexus.
3. Put the token copy of Ugin's Nexus into exile due to the legend rule, causing you to take an extra turn after this one.
4. Resolve the Teferi's Realm trigger, causing Ugin's Nexus and Mechanized Production to phase out.
5. Move to your next turn.
6. At the beginning of your untap step, Mechanized Production and Ugin's Nexus phase in.
7. Repeat.