Breath of Fury attached to any other creature you control that can attack this turn and that cannot be blocked by an opponent.
Helm of the Host attached to any creature except the creature that has
Breath of Fury attached.
Steps
At the beginning of your combat phase,
Helm of the Host triggers, creating a nonlegendary token copy of the creature it is attached to with haste.
Deal combat damage to an opponent 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 token created in step 1, then causing you to untap all creatures you control and to get an additional combat phase after this one.
Repeat each combat phase.
Results
Infinite combat damage.
Infinite combat phases.
Infinite death triggers.
Infinite creature ETB.
Infinite creature LTB.
Infinite mana creatures you control can produce.
Infinite creature sacrifice triggers.
Infinite untap of creatures you control.
Metadata
Bracket tag
SpicyBracket 3-4+
Probably 3 or 4, but hard to classify
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5
1 · Exhibition5 · cEDH
Bracket tags are estimated from the cards and results of each combo, as a guideline rather than a strict classification.