Infinite combat damageInfinite combat phasesInfinite death triggersInfinite creature ETBInfinite creature LTBInfinite mana creatures you control can produceInfinite creature sacrifice triggersInfinite untap of creatures you control
How it works
Declare the creature with Breath of Fury attached as an attacker.
Doors of Durin triggers, causing you to scry 2, ensuring to leave the creature card with haste on top of your library, then revealing the creature card and putting it onto the battlefield tapped and attacking.
Deal combat damage using the creature that has Breath of Fury attached.
Breath of Fury triggers, causing you to sacrifice the creature it is attached to, then attach Breath of Fury to the creature Doors of Durin returned, then causing you to untap all creatures you control and to get an additional combat phase after this one.
When the creature dies, Mortuary triggers, putting the creature on top of your library from your graveyard.
Repeat each combat phase.
This looping setup hinges on the relentless engine of Breath of Fury, which constantly refreshes your army and grants endless extra combat phases every time its enchanted creature connects with a player. To sustain this, Doors of Durin steps in during each attack to reliably scry your deck and cheat a fresh creature straight onto the battlefield, ready to absorb the Aura next. Meanwhile, Mortuary ensures the sacrificed creature never truly stays dead, neatly recycling it to the top of your library so Doors of Durin can immediately find and redeploy it for the next assault.