Aspiring Champion + Blightsteel Colossus + Worldly Tutor + Leyline of Transformation

How it works

Aspiring Champion does not have summoning sickness, and cannot be blocked by an opponent.
"Demon" chosen with Leyline of Transformation.

Cast Worldly Tutor by paying , searching your library for Blightsteel Colossus and putting it on top of your library.
Deal combat damage to an opponent using Aspiring Champion.
Aspiring Champion triggers, causing you to sacrifice it, then reveal Blightsteel Colossus from the top of your library and put it onto the battlefield as a Demon due to Leyline of Transformation, then causing Blightsteel Colossus to give each opponent eleven poison counters.
Each opponent loses the game as a state-based action due to having ten or more poison counters.

In which brackets is this combo allowed, per Spellbook's Powerful tier?

1–2 · Exhibition & Core

Spellbook classifies this as Powerful — not for these brackets.

3 · Upgraded

Allowed in this bracket.

4–5 · Optimized & cEDH

All combos are allowed.