Activate Fanatical Firebrand by tapping and sacrificing it.
When Fanatical Firebrand dies, Mortuary and Ashes of the Abhorrent trigger.
Resolve the Mortuary trigger, putting Fanatical Firebrand from your graveyard onto the top of your library.
Resolve the Ashes of the Abhorrent trigger, causing you to gain 1 life
Resolve the Fanatical Firebrand ability.
Cast Fanatical Firebrand from the top of your library by paying 1 life.
Repeat.
This ingenious loop turns a humble goblin into a repeating engine of destruction by manipulating the top of your library. When you tap and sacrifice Fanatical Firebrand, Mortuary steps in to immediately catch it from the graveyard and tuck it neatly back onto your library, while Ashes of the Abhorrent gently cushions the self-inflicted blow by ticking your life total back up every time a creature dies. Meanwhile, Gwenom, Remorseless is the key that lets you bypass normal casting restrictions, allowing you to cast the Firebrand straight off the top of your deck while trading mana costs for life.