Sekki, Seasons' Guide + Pandemonium

Decks

How it works

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Cast Sekki by paying .
When Sekki enters, Pandemonium triggers, targeting Sekki. Sekki prevents the 8 damage that would be dealt to it and instead removes eight +1/+1 counters from Sekki and creates eight 1/1 Spirit creature tokens.
Sekki dies as a state-based action due to having 0 toughness.
When the Spirits enter, Pandemonium triggers that many times, dealing a total of 8 damage divided among any number of targets.
Activate Sekki by sacrificing the eight Spirit tokens, returning Sekki from your graveyard to the battlefield.
Repeat from step 2.

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

1–2 · Exhibition & Core

Spellbook classifies this as Powerful — not for these brackets.

3 · Upgraded

Allowed in this bracket.

4–5 · Optimized & cEDH

All combos are allowed.