Ugin's Nexus + Aetheric Amplifier + Karn, the Great Creator + Krark-Clan Ironworks

Ugin's Nexus

Aetheric Amplifier

Karn, the Great Creator

Krark-Clan Ironworks

How it works

1. If Karn has exactly one loyalty counter on it, activate its first loyalty ability by putting a loyalty counter on it.
2. Activate Krark-Clan Ironworks by sacrificing Ugin's Nexus. Ugin's Nexus will be exiled instead of being put into your graveyard due to its replacement effect, causing you to take an extra turn after this one.
3. Move to your next turn.
4. Activate Aetheric Amplifier by paying 4 and tapping it, doubling the number of counters on Karn.
5. Activate Karn's second loyalty ability by removing two loyalty counters from it, returning Ugin's Nexus from exile to your hand.
6. Cast Ugin's Nexus by paying 5.
7. Repeat from step 2.

This ingenious loop achieves an endless chain of extra turns by turning Ugin's Nexus into a recurring resource, powered by the mana-generating engine of Krark-Clan Ironworks. Because Ugin's Nexus is exiled rather than hitting the graveyard, it gets trapped in exile where Karn, the Great Creator can easily pluck it back to your hand using its minus ability. To keep Karn from running out of fuel, Aetheric Amplifier steps in to double Karn's loyalty counters, ensuring you always have enough energy to retrieve the Nexus and cast it again.