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

Medomai the Ageless

Idris, Soul of the TARDIS

Karn's Bastion

Silverskin Armor

How it works

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

This clever loop bypasses Medomai the Ageless's restriction against attacking during extra turns by turning Idris, Soul of the TARDIS into a clever mechanical copy. By equipping Silverskin Armor to Medomai, you ensure it counts as an artifact so Idris can successfully imprint it upon entering the battlefield. Once Idris inherits Medomai's combat-damage trigger, it can swing for extra turns without the self-referential clause that normally stops Medomai. To keep Idris from fading away via its own Vanishing 3, you simply use Karn's Bastion to proliferate time counters back onto it, locking in an endless succession of extra turns.