Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Umbral Collar Zealot + Arcbound Whelp

Decks

How it works

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Activate Umbral Collar Zealot by sacrificing Arcbound Whelp.
When Arcbound Whelp dies, its modular ability and persist ability trigger.
Resolve the modular trigger, putting Arcbound Whelp's +1/+1 counters on another artifact creature.
Resolve the persist trigger, returning Arcbound Whelp from your graveyard to the battlefield. It will not have a -1/-1 counter on it due to its modular ability.
Resolve the Umbral Collar Zealot ability.
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.