Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight + Blasting Station + Towering Titan

How it works

—

Activate Blasting Station by tapping it and sacrificing Towering Titan.
When Towering Titan dies, its persist ability triggers, returning it from your graveyard to the battlefield without a -1/-1 counter on it due to its replacement effect.
When Towering Titan enters, Blasting Station triggers, untapping Blasting Station.
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.