Ugin's Nexus + Aetheric Amplifier + Karn, the Great Creator + Bartolomé del Presidio

Ugin's Nexus

Aetheric Amplifier

Karn, the Great Creator

Bartolomé del Presidio

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 Bartolomé del Presidio 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 intricate artifact loop locks down your opponents and grants you infinite turns by endlessly recycling Ugin's Nexus. By using Karn, the Great Creator's +1 ability, you turn Ugin's Nexus into an artifact creature so that Bartolomé del Presidio can easily sacrifice it; this triggers the Nexus's replacement effect to exile itself and grant you an extra turn. Once you are in that extra turn, Aetheric Amplifier steps in to double Karn's loyalty counters for a modest mana investment, allowing Karn's −2 ability to pull Ugin's Nexus right back out of exile and into your hand to be recast.