Sepulchral Primordial + Infinite Reflection + Phyrexian Altar

How it works

You have a way to cause a nontoken creature to enter the battlefield under your control.
An opponent has a creature card in their graveyard.

Cause a nontoken creature to enter the battlefield under your control, which enters as a copy of Sepulchral Primordial due to Infinite Reflection.
When the creature enters, it triggers. Holding priority, activate Phyrexian Altar by sacrificing the creature.
Resolve the creature's trigger, putting a creature card from an opponent's graveyard onto the battlefield under your control as a copy of Sepulchral Primordial.
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.