The Legend of Kuruk // Avatar Kuruk + Sakashima of a Thousand Faces + The Mind Stone

Decks

How it works

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Activate Sakashima of a Thousand Faces using Avatar Kuruk's ability by paying minus for each creature and/or artifact you can tap while activating it, causing you to take an extra turn after this one.
At the beginning of your end step, The Mind Stone triggers, blinking Sakashima of a Thousand Faces. Choose to have it enter the battlefield as a copy of Avatar Kuruk.
Repeat each turn.

In which brackets is this combo allowed, per Spellbook's Ruthless tier?

1–2 · Exhibition & Core

Spellbook classifies this as Ruthless — not for these brackets.

3 · Upgraded

Spellbook classifies this as Ruthless — not for these brackets.

4–5 · Optimized & cEDH

All combos are allowed.