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

Ugin's Nexus

Aetheric Amplifier

Karn, the Great Creator

Krark-Clan Grunt

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 Grunt 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 gives you all the time in the world by weaponizing Ugin's Nexus's own graveyard-exile replacement effect to trigger an extra turn, while making sure you never actually run out of copies to cast. Once Ugin's Nexus is sacrificed to fuel Krark-Clan Grunt, it safely lands in exile rather than the graveyard, setting up your next sequence. From there, Aetheric Amplifier steps in to effortlessly double Karn, the Great Creator's loyalty counters—turning a single activation cost into an engine that easily sustains Karn's minus ability. Karn then reaches into exile to pull Ugin's Nexus right back to your hand, ready to be recast and sacrificed all over again.