Megaton's Fate + Dualcaster Mage + Lilysplash Mentor + Artifact that is Indestructible

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How it works

Cast Megaton's Fate by paying , targeting the indestructible artifact.
Holding priority, activate Lilysplash Mentor by paying , blinking Dualcaster Mage.
When Dualcaster Mage enters the battlefield, it triggers, copying Megaton's Fate, with the copy targeting the indestructible artifact.
Resolve the copy of Megaton's Fate, failing to destroy the artifact due to it being indestructible, and creating four Treasure tokens.
Activate three Treasure tokens by tapping and sacrificing them, adding .
Repeat from step 2.

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.