Opalescence + Yenna, Redtooth Regent + Doubling Season + Infinite Reflection + Inventive Iteration // Living Breakthrough

Exhibition

How it works

Activate Yenna by paying and tapping it, creating two token copies of Doubling Season.
Cast Infinite Reflection by paying , attaching it to Inventive Iteration.
When Infinite Reflection enters the battlefield, it triggers, causing each nontoken creature you control to become a copy of Inventive Iteration.
Cast any transforming double-faced creature or enchantment card by paying its mana cost, causing it to enter the battlefield as a copy of Inventive Iteration with four chapter counters due to Infinite Reflection and the Doubling Season tokens.
The creature or enchantment's first, second and third chapter abilities trigger.
Resolve the first and second triggers, returning up to one creature or planeswalker to its owner's hand, and then either returning an artifact card from your graveyard to your hand or causing you to draw a card.
Resolve the third trigger, exiling the creature or enchantment, and returning it to the battlefield transformed as a copy of Inventive Iteration with four chapter counters due to Infinite Reflection and the Doubling Season tokens.
Repeat from step 5.
When your library is down to one card remaining, use the creature's first trigger to return the original Inventive Iteration to your hand, thus ending the loop.

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.

How it works

Activate Yenna by paying and tapping it, creating two token copies of Doubling Season.
Cast Infinite Reflection by paying , attaching it to Inventive Iteration.
When Infinite Reflection enters the battlefield, it triggers, causing each nontoken creature you control to become a copy of Inventive Iteration.
Cast any transforming double-faced creature or enchantment card by paying its mana cost, causing it to enter the battlefield as a copy of Inventive Iteration with four chapter counters due to Infinite Reflection and the Doubling Season tokens.
The creature or enchantment's first, second and third chapter abilities trigger.
Resolve the first and second triggers, returning up to one creature or planeswalker to its owner's hand, and then either returning an artifact card from your graveyard to your hand or causing you to draw a card.
Resolve the third trigger, exiling the creature or enchantment, and returning it to the battlefield transformed as a copy of Inventive Iteration with four chapter counters due to Infinite Reflection and the Doubling Season tokens.
Repeat from step 5.
When your library is down to one card remaining, use the creature's first trigger to return the original Inventive Iteration to your hand, thus ending the loop.