Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Ashnod's Altar + Stormbound Geist

How it works

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Activate Ashnod's Altar by sacrificing Stormbound Geist
When Stormbound Geist dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Activate Ashnod's Altar by sacrificing Stormbound Geist
When Stormbound Geist dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Repeat.

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

1–2 · Exhibition & Core

Spellbook classifies this as Spicy — not for these brackets.

3 · Upgraded

Allowed in this bracket.

4–5 · Optimized & cEDH

All combos are allowed.