The Legend of Kuruk // Avatar Kuruk + Marvin, Murderous Mimic + Baboon Spirit

Decks

How it works

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Activate Marvin 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 Marvin.
At the beginning of your end step, Baboon Spirit triggers, returning Marvin from exile to the battlefield
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.