Baba Lysaga, Night Witch + Dross Scorpion + Thran Vigil + Cauldron of Souls + Biotransference

Decks

How it works

You control two additional nontoken creatures, one of which has another card type besides artifact or creature.
The additional nontoken creatures have base toughness 2 or greater and do not have a -1/-1 counter on them.

Activate Cauldron of Souls by tapping it, giving the additional creatures persist until end of turn.
Activate Baba Lysaga by tapping it and sacrificing the two additional creatures.
When the creatures die, Dross Scorpion triggers twice and the creatures' persist abilities each trigger.
Resolve the Dross Scorpion triggers, untapping Baba Lysaga and Cauldron of Souls.
Resolve the first persist creature, returning one of the creatures from your graveyard to the battlefield with a -1/-1 counter on it.
When the creature enters, Thran Vigil triggers, putting a +1/+1 counter on the creature.
Repeat from step 5 for the remaining persist trigger.
Resolve the Baba Lysaga ability from step 2, causing you to gain 3 life, each opponent to lose 3 life, and you to draw three cards.
Repeat.

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.