Ugin's Nexus + Esoteric Duplicator + Sarcatog

Ugin's Nexus

Esoteric Duplicator

Sarcatog

How it works

1. During your end step, activate Sarcatog's second ability by sacrificing Ugin's Nexus.
2. Ugin's Nexus is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
3. Esoteric Duplicator triggers, causing you to pay 2 to create a token copy of Ugin's Nexus at the beginning of your next end step.
4. Resolve the Sarcatog ability, giving it +1/+1 until end of turn.
5. Move to your extra turn.
6. At the beginning of your end step, Esoteric Duplicator triggers, creating a token copy of Ugin's Nexus.
7. Repeat.

This clever loop locks down extra turns while generating an endless supply of them right under your opponents' noses. By using Sarcatog's sacrifice ability to feed Ugin's Nexus to the graveyard, the Nexus's own replacement effect exiles it instead while rewarding you with an extra turn. Simultaneously, Esoteric Duplicator watches your artifacts head to the yard and lets you pay {2} to seed a token copy of the Nexus for the upcoming end step. Because Ugin's Nexus prevents *future* extra turns only if a player would begin them, timing the creation of these token copies during the end step sidesteps that restriction completely, letting you chain endless turns together.