Osgir, the Reconstructor + Karn, the Great Creator + Ugin's Nexus + Noose Constrictor + Bard, King of Dale

Osgir, the Reconstructor

Karn, the Great Creator

Ugin's Nexus

Noose Constrictor

Bard, King of Dale

How it works

1. Activate Osgir by paying 5, tapping it and exiling Ugin's Nexus from your graveyard, creating four token copies of Ugin's Nexus.
2. Put three of the Ugin's Nexus tokens into exile due to the legend rule and their replacement effects, causing you to take three extra turns after this one.
3. Activate Karn's first loyalty ability by putting a loyalty counter on it, choosing to do nothing.
4. Move to your next extra turn.
5. Repeat from step 3 one additional time.
6. Activate Karn's second loyalty ability by removing two loyalty counters from it, returning Ugin's Nexus from exile to your hand.
7. Activate Noose Constrictor by discarding Ugin's Nexus.
8. Move to your last extra turn.
9. Repeat.

This intricate sequence locks down the game by chaining infinite extra turns through clever graveyard and exile manipulation. Osgir, the Reconstructor acts as the primary engine, using its activation to duplicate Ugin's Nexus so that its replacement effect triggers multiple extra turns simultaneously. Meanwhile, Bard, King of Dale supercharges Osgir's replication by doubling the token creation, turning a single exile into a game-winning hoard. To sustain the loop, Karn, the Great Creator reaches into exile to retrieve Ugin's Nexus, allowing Noose Constrictor to neatly discard it back into the graveyard where Osgir can start the process all over again.