Demon's Disciple enters the battlefield, it triggers.
Holding priority, activate
Relic of Legends' second ability by tapping
Burakos, adding ({B} magic symbol) .
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
Demon's Disciple trigger from step 2, causing you to sacrifice
Burakos, and each opponent to sacrifice a creature or planeswalker.
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 ({B} magic symbol) and removing the +1/+1 counter from
Burakos, giving
Demon's Disciple -1/-1 until end of turn.
Demon's Disciple 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 ({B} magic symbol) and removing the +1/+1 counter from
Burakos and
Demon's Disciple, giving
Demon's Disciple -2/-2 until end of turn.
Repeat from step 8.
Results
Each opponent sacrifices all creatures they control.
Each opponent sacrifices all planeswalkers they control.
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinitely powerful Orcs, Wizards, Warriors, Rogues, and Clerics except