Carth the Lion + Liliana Vess + Nexus of Fate + Irenicus's Vile Duplication

How it works

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Cast Irenicus's Vile Duplication by paying , creating a nonlegendary copy of Carth the Lion with flying.
Cast Nexus of Fate by paying , causing you to take an extra turn after this one and shuffle Nexus of Fate into your library.
Activate Liliana Vess's second loyalty ability by removing zero loyalty counters from it, searching your library for Nexus of Fate, then shuffling your library and putting it on top.
Move to your next turn, drawing Nexus of Fate during your draw step.
Repeat from step 2.

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

1–2 · Exhibition & Core

Spellbook classifies this as Ruthless — not for these brackets.

3 · Upgraded

Spellbook classifies this as Ruthless — not for these brackets.

4–5 · Optimized & cEDH

All combos are allowed.