Ugin's Nexus + Aetheric Amplifier + Karn, the Great Creator + Sarcatog

Ugin's Nexus

Aetheric Amplifier

Karn, the Great Creator

Sarcatog

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 Sarcatog 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 fascinating loop locks down extra turns while generating an endless sequence of them using a clever recursive artifact engine. Sarcatog acts as the sacrifice outlet that sends Ugin's Nexus to exile instead of the graveyard, triggering its replacement effect to grant you an extra turn. Once Ugin's Nexus is safely in exile, Karn, the Great Creator uses its minus ability to retrieve it back to your hand so you can recast it. Meanwhile, Aetheric Amplifier fuels this engine by doubling the loyalty counters on Karn so it always has the energy needed to keep pulling the nexus back.