Medomai the Ageless + Idris, Soul of the TARDIS + Jhoira's Timebug + Ashnod's Transmogrant

Medomai the Ageless

Idris, Soul of the TARDIS

Jhoira's Timebug

Ashnod's Transmogrant

How it works

1. Activate Ashnod's Transmogrant by tapping and sacrificing it, putting a +1/+1 counter on Medomai the Ageless and causing it 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. Activate Jhoira's Timebug by tapping it, putting a time counter on Idris.
7. Move to your extra turn.
8. At the beginning of your upkeep, Idris's vanishing ability triggers, removing a time counter from it.
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.

This brilliant loop turns Medomai the Ageless into a permanent engine for infinite extra turns by using Ashnod's Transmogrant to permanently transform Medomai into an artifact creature. Once exiled by Idris, Soul of the TARDIS upon its entry, Idris cleverly copies Medomai's combat damage trigger while shedding Medomai's restriction against attacking during extra turns. Finally, Jhoira's Timebug steps in to manipulate time counters on Idris, continually resetting its vanishing timer during upkeep so the copied terror can keep striking for turn after turn without ever fading away.