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

Medomai the Ageless

Idris, Soul of the TARDIS

Karn's Bastion

Liquimetal Torque

How it works

1. Activate Liquimetal Torque's second ability by tapping it, causing Medomai the Ageless to become an artifact until end of turn.
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 turning Medomai the Ageless into an artifact with Liquimetal Torque, you can cleanly exile it beneath Idris, Soul of the TARDIS when Idris enters the battlefield. This grants Idris all of Medomai's abilities—including the crucial combat damage trigger for extra turns—while entirely bypassing Medomai’s restriction against attacking during extra turns since you are attacking with Idris instead! To keep this infinite loop sustained before Idris phases away or runs out of time, Karn's Bastion steps in to proliferate and replenish the vanishing counters on Idris during your upkeep.