Medomai the Ageless + Idris, Soul of the TARDIS + Karn's Bastion + Memnarch

Medomai the Ageless

Idris, Soul of the TARDIS

Karn's Bastion

Memnarch

How it works

1. Activate Memnarch's first ability by paying 1, causing Medomai the Ageless to become an artifact.
2. Deal combat damage to an opponent using Medomai the Ageless.
3. Medomai the Ageless triggers, causing you to take an extra turn after this one.
4. Cast Idris by paying 1.
5. When Idris enters the battlefield, it triggers, exiling Medomai the Ageless until Idris leaves the battlefield.
6. Move to your extra turn.
7. At the beginning of your upkeep, Idris's vanishing ability triggers, removing a time counter from it.
8. Activate Karn's Bastion's second ability by paying 4 and tapping it, putting a time counter on Idris.
9. Deal combat damage to an opponent using Idris.
10. Idris triggers, causing you to take an extra turn after this one.
11. Repeat from step 6.

By leveraging Memnarch to turn Medomai the Ageless into an artifact, you can safely exile it under Idris, Soul of the TARDIS as it enters the battlefield, allowing Idris to cleanly inherit Medomai's devastating extra-combat-turn trigger without inheriting Medomai's pesky restriction against attacking during extra turns. This means Idris can swing freely to chain infinite turns, all while Karn's Bastion steps in to constantly replenish Idris's vanishing time counters and prevent it from accidentally slipping away.