Carmen, Cruel Skymarcher + Leonin Relic-Warder + All-Out Assault + Phyrexian Altar

Decks

How it works

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Cast All-Out Assault by paying .
When All-Out Assault enters the battlefield, it triggers, causing you to get an additional combat and main phase after this one.
Move to your extra combat phase. All-Out Assault triggers, untapping each creature you control.
Declare Carmen as an attacker, triggering its second ability, returning Leonin Relic-Warder form your graveyard to the battlefield.
When Leonin Relic-Warder enters the battlefield, its first ability triggers, exiling All-Out Assault.
Move to your postcombat main phase, and activate Phyrexian Altar by sacrificing Leonin Relic-Warder, adding one mana of any color.
When Leonin Relic-Warder dies, its second ability and Carmen's first ability trigger.
Resolve the Carmen trigger, putting a +1/+1 counter on it and causing you to gain 1 life.
Resolve the Leonin Relic-Warder trigger, returning All-Out Assault from exile to the battlefield.
When All-Out Assault enters the battlefield, it triggers, causing you to get an additional combat and main phase after this one.
Repeat from step 3.

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.