Burakos, Party Leader + Haunted One + Relic of Legends + Merciless Executioner + Retribution of the Ancients

Exhibition

How it works

Cast Merciless Executioner by paying .
When Merciless Executioner enters the battlefield, it triggers.
Holding priority, activate Relic of Legends' second ability by tapping Burakos, adding .
Burakos triggers, giving it and all creatures you control that share a creature type with it +2/+0 and undying until end of turn.
Resolve the Merciless Executioner trigger from step 2, causing you to sacrifice Burakos, and each opponent to sacrifice a creature.
When Burakos dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Activate Retribution of the Ancients by paying and removing the +1/+1 counter from Burakos, giving Merciless Executioner -1/-1 until end of turn.
Merciless Executioner dies as a state-based action due to having 0 toughness, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter from it.
Repeat steps 2 through 6 one additional time.
Activate Retribution of the Ancients by paying and removing the +1/+1 counter from Burakos and Merciless Executioner, giving Merciless Executioner -2/-2 until end of turn.
Repeat from step 8.

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.

How it works

Cast Merciless Executioner by paying .
When Merciless Executioner enters the battlefield, it triggers.
Holding priority, activate Relic of Legends' second ability by tapping Burakos, adding .
Burakos triggers, giving it and all creatures you control that share a creature type with it +2/+0 and undying until end of turn.
Resolve the Merciless Executioner trigger from step 2, causing you to sacrifice Burakos, and each opponent to sacrifice a creature.
When Burakos dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Activate Retribution of the Ancients by paying and removing the +1/+1 counter from Burakos, giving Merciless Executioner -1/-1 until end of turn.
Merciless Executioner dies as a state-based action due to having 0 toughness, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter from it.
Repeat steps 2 through 6 one additional time.
Activate Retribution of the Ancients by paying and removing the +1/+1 counter from Burakos and Merciless Executioner, giving Merciless Executioner -2/-2 until end of turn.
Repeat from step 8.