Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Flayer of the Hatebound + Umbral Collar Zealot

Decks

How it works

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Activate Umbral Collar Zealot by sacrificing Flayer of the Hatebound
When Flayer of the Hatebound dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When Flayer of the Hatebound enters, it triggers, dealing damage equal to its power to any target.
Activate Umbral Collar Zealot by sacrificing Flayer of the Hatebound
When Flayer of the Hatebound dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Flayer of the Hatebound enters, it triggers, dealing damage equal to its power to any target.
Resolve both Umbral Collar Zealot abilities from step 1 and 4.
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.