Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Blasting Station + Wakandan Royal Guard

How it works

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Activate Blasting Station by tapping it and sacrificing Wakandan Royal Guard.
When Wakandan Royal Guard dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Wakandan Royal Guard enters, it and Blasting Station trigger.
Resolve the Wakandan Royal Guard trigger, putting a +1/+1 counter on it
Resolve the Blasting Station trigger, untapping it.
Resolve the Blasting 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.