Luminous Broodmoth + Nardole, Resourceful Cyborg + Grinding Station

Decks

How it works

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Activate Grinding Station by tapping it and sacrificing Nardole.
When Nardole dies, its undying ability triggers if it didn't have a +1/+1 counter, and Luminous Broodmoth triggers if Nardole didn't have flying.
Resolve the undying trigger, if applicable, returning Nardole from your graveyard to the battlefield with either a +1/+1 counter on it.
If Nardole entered the battlefield in step 3, Grinding Station triggers, untapping Grinding Station.
Resolve the Luminous Broodmoth trigger, if applicable, returning Nardole from your graveyard to the battlefield with a flying counter on it if the creature is still in your graveyard.
If Nardole entered the battlefield in step 5, Grinding Station triggers, untapping Grinding Station.
Resolve the Grinding Station ability from step 1.
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.