Herigast, Erupting Nullkite + Cloudstone Curio + Molten Echoes + Nonartifact, Nonlegendary Creature with a Generic Mana Cost

Exhibition

Decks

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How it works

You have enough mana to cast the creature with a generic mana cost either for its mana cost, or for its emerge cost.
Molten Echoes naming any type that appears on the creature with a generic mana cost.
Nonartifact, Nonlegendary Creature with a Generic Mana Cost

Cast the creature with a generic mana cost by paying its mana cost or emerge cost.
When the creature enters the battlefield, Cloudstone Curio and Molten Echoes trigger.
Resolve the Cloudstone Curio trigger, choosing to return nothing to your hand.
Resolve the Molten Echoes trigger, creating a token copy of the generic mana cost creature.
When the creature token enters the battlefield, Cloudstone Curio triggers, returning the nontoken generic mana cost creature from the battlefield to your hand.
Cast the generic mana cost creature for its emerge cost by sacrificing the creature token created in step 5, and by paying as the token will have the same mana value.
Repeat from step 2.

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

1–2 · Exhibition & Core

Allowed in this bracket.

3 · Upgraded

Allowed in this bracket.

4–5 · Optimized & cEDH

All combos are allowed.