Ugin's Nexus | Esoteric Duplicator | Krark-Clan Ironworks

Cards

During your end step, activate
Krark-Clan Ironworks by sacrificing
Ugin's Nexus, adding ({C} magic symbol) ({C} magic symbol) .
Ugin's Nexus is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
Esoteric Duplicator triggers, causing you to pay ({2} magic symbol) to create a token copy of
Ugin's Nexus at the beginning of your next end step.
Move to your extra turn.
At the beginning of your end step,
Esoteric Duplicator triggers, creating a token copy of
Ugin's Nexus.
Repeat.

This combo has been estimated to be Ruthless (Bracket 4+).