Activate Kiki-Jiki by tapping it, creating a token copy of Goblin Firestarter with haste.
Activate a Goblin Firestarter you control by sacrificing it.
Kiki-JIki triggers, untapping itself.
Resolve the Goblin Firestarter ability, dealing 1 damage to any target.
Repeat.

Infinite damage

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite sacrifice triggers

Kiki-Jiki, Mirror Breaker

Thornbite Staff

Goblin Firestarter

Cast Doomsday by paying {B}{B}{B}, searching your library and graveyard for Torch Courier, Kiki-Jiki, Goblin Firestarter, Brazen Buccaneers and Conspicuous Snoop, exiling all other cards from your graveyard and library, and then placing the remaining cards on top of your library in the order previously listed and losing half your life, rounded up.
Activate Grenzo by paying {2}, putting Conspicuous Snoop into your graveyard and then onto the battlefield.
Cast Torch Courier from the top of your library by paying {R}.
Activate Torch Courier by sacrificing it, giving Conspicuous Snoop haste until end of turn.
Activate Conspicuous Snoop using Kiki-Jiki's ability by tapping it, creating a token copy of Conspicuous Snoop with haste.
Repeat step 5 with the new Conspicuous Snoop token an arbitrarily large amount of times.
Activate Grenzo by paying {2}, putting Brazen Buccaneers into your graveyard and then onto the battlefield.
Brazen Buccaneers enters the battlefield, revealing Kiki-Jiki, putting a +1/+1 counter on Brazen Buccaneers and putting Kiki-Jiki into your graveyard.
Activate a Conspicuous Snoop using Goblin Firestarter's ability by sacrificing it, dealing 1 damage to any target.
Repeat from step 9.

Each opponent loses the game

Infinite creature tokens with haste

Doomsday

Grenzo, Dungeon Warden

Conspicuous Snoop

Torch Courier

Brazen Buccaneers

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

Solemnity

Luminous Broodmoth

Activate Goblin Firestarter by sacrificing it.
When Goblin Firestarter dies, Mortuary and South Wind Avatar trigger.
Resolve the Mortuary trigger, putting Goblin Firestarter 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 Goblin Firestarter ability.
Cast Goblin Firestarter from the top of your library by paying 1 life.
Repeat.

Infinite lifegain triggers

Infinite storm count

Infinite lifeloss

Mortuary

South Wind Avatar

Gwenom, Remorseless

Activate Goblin Firestarter by sacrificing it.
When Goblin Firestarter 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 Goblin Firestarter ability.
Repeat.

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

Vizier of Remedies

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

Infinite green mana

Infinite landfall triggers

Zimone, Mystery Unraveler

Yedora, Grave Gardener

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

Ratadrabik of Urborg

Leyline of Singularity

Activate a basic Swamp by tapping it, adding {B}.
Activate Kenrith's fifth ability by paying {B} due to Agatha, returning Goblin Firestarter from your graveyard to the battlefield.
Activate Earthcraft by tapping Goblin Firestarter, untapping the basic Swamp.
Activate Goblin Firestarter by sacrificing it.
Repeat.

Kenrith, the Returned King

Earthcraft

Agatha of the Vile Cauldron

Combos with "Goblin Firestarter"