There and Back Again + Orvar, the All-Form + Imps' Taunt

Exhibition

How it works

At the beginning of your precombat main phase, There and Back Again triggers, creating a legendary 6/6 Smaug creature token, and causing you to sacrifice There and Back Again.
Cast Imps' Taunt with buyback by paying , targeting the Smaug token.
Orvar's first ability triggers, creating a copy of the Smaug token.
Put the new Smaug token into your graveyard due to the legend rule.
When Smaug dies, it triggers, creating fourteen Treasure tokens.
Resolve Imps' Taunt from step 2, returning it to your hand.
Activate five Treasures by tapping and sacrificing them, adding .
Repeat from step 2.
Once you have infinite colored mana, you may instead target any other creature(s) you control using Imps' Taunt, to create infinite tokens of them using Orvar.

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.