Activate Fanatical Firebrand by tapping and sacrificing it.
When Fanatical Firebrand dies, Luminous Broodmoth triggers, returning Fanatical Firebrand from your graveyard to the battlefield without a flying counter on it due to Solemnity.
Resolve the Fanatical Firebrand ability.
Repeat.

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite sacrifice triggers

Infinite damage

Solemnity

Luminous Broodmoth

Fanatical Firebrand

Activate Fanatical Firebrand by tapping it and sacrificing it.
When Fanatical Firebrand dies, Mortuary and South Wind Avatar trigger.
Resolve the Mortuary trigger, putting Fanatical Firebrand from your graveyard onto the top of your library.
Resolve the South Wind Avatar trigger, causing you to gain 1 life.
South Wind Avatar triggers, causing each opponent to lose 1 life.
Resolve the Fanatical Firebrand ability.
Cast Fanatical Firebrand from the top of your library by paying 1 life.
Repeat.

Infinite lifegain triggers

Infinite storm count

Infinite lifeloss

Mortuary

South Wind Avatar

Bolas's Citadel

Activate Fanatical Firebrand by tapping it and sacrificing it.
When Fanatical Firebrand dies, its persist ability triggers, returning it from your graveyard to the battlefield without a -1/-1 counter on it due to Vizier of Remedies.
Resolve the Fanatical Firebrand ability.
Repeat.

Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight

Vizier of Remedies

Activate Fanatical Firebrand by tapping and sacrificing it.
When Fanatical Firebrand dies, Yedora triggers, returning Fanatical Firebrand from your graveyard to the battlefield face-down as a Forest land.
When Fanatical Firebrand enters the battlefield, Zimone triggers.
Holding priority, activate Fanatical Firebrand by tapping it, adding {G}.
Resolve the Zimone trigger, turning Fanatical Firebrand face-up.
Resolve the Fanatical Firebrand ability from step 1.
Repeat.

Infinite green mana

Infinite landfall triggers

Zimone, Mystery Unraveler

Yedora, Grave Gardener

Activate Fanatical Firebrand by tapping and sacrificing it.
When Fanatical Firebrand dies, Ratadrabik triggers, creating a token copy of Fanatical Firebrand that is a 2/2 legendary Zombie in addition to its other types.
Resolve the Fanatical Firebrand ability.
Repeat using the Fanatical Firebrand token

Ratadrabik of Urborg

Leyline of Singularity

Combos with "Fanatical Firebrand"