Sigil of the New Dawn + Mana Echoes + Siege-Gang Commander + Urn of Godfire

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How it works

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Cast Siege-Gang Commander by paying .
When Siege-Gang Commander enters the battlefield, it and Mana Echoes trigger.
Resolve the Siege-Gang Commander trigger, creating three 1/1 Goblin creature tokens.
When the Goblin tokens enter the battlefield, Mana Echoes triggers three times.
Resolve all four Mana Echoes triggers, adding at least .
Activate Urn of Godfire four times by paying , adding .
Activate Siege-Gang Commander by paying and sacrificing itself.
Sigil of the New Dawn triggers, causing you to pay to return Siege-Gang Commander from your graveyard to your hand.
Resolve the Siege-Gang Commander activated ability, dealing 2 damage to any target.
Repeat.

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.