Ugin's Nexus + Esoteric Duplicator + Krark-Clan Grunt

Ugin's Nexus

Esoteric Duplicator

Krark-Clan Grunt

How it works

1. During your end step, activate Krark-Clan Grunt 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 Krark-Clan Grunt ability.
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.