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

Ugin's Nexus

Aetheric Amplifier

Karn, the Great Creator

Lithatog

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 Lithatog 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 clever loop turns Ugin's Nexus into a renewable source of endless time by exploiting its exile-and-extra-turn replacement effect rather than letting it rest in the graveyard. Lithatog acts as the crucial sacrifice outlet that triggers this effect on demand, sending Ugin's Nexus to exile instead of the graveyard. Once exiled, Karn, the Great Creator retrieves the artifact right back to your hand using its minus ability, bypassing its usual exile-fetching limits to keep the chain unbroken. Aetheric Amplifier powers this engine by doubling Karn's loyalty counters, ensuring Karn always has the fuel required to repeatedly fish Ugin's Nexus out of exile and start the cycle anew.