Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Geralf's Mindcrusher + Carrion Feeder

Decks

How it works

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Activate Carrion Feeder by sacrificing Geralf's Mindcrusher
When Geralf's Mindcrusher dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When Geralf's Mindcrusher enters, it triggers, causing a player to mill five cards.
Activate Carrion Feeder by sacrificing Geralf's Mindcrusher
When Geralf's Mindcrusher dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Geralf's Mindcrusher enters, it triggers, causing a player to mill five cards.
Resolve both Carrion Feeder 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.