The Legend of Kuruk // Avatar Kuruk + Sakashima the Impostor + Baboon Spirit

Decks

How it works

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Activate Sakashima the Impostor 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.
Activate Baboon Spirit by paying , exiling Sakashima
At the beginning of your end step, Baboon Spirit triggers, returning Sakashima from exile to the battlefield. 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.