Introduction:

8-whack is a aggressive budget goblin deck that can be very explosive and powerful. The name comes from the cards
Goblin Bushwhacker(which was the first iteration from Zendikar) and Reckless Bushwhacker (from Oath of the Gatewatch). The deck often uses tiny creatures to pump up with a Bushwhacker and attack for a big chunk of damage.

It doesn't need to be a tribal deck but many cards that make the deck powerful such as the Bushwhacker's also uses Legion Goblin Guide, Loyalist and
Foundry Street Denizen that gives the deck more power are also goblins.

Card Discussion Main:

Mogg Fanatic, Fanatical Firebrand and Goblin Arsonist:
This is something people see and often say, play Mogg Fanatic, the other two suck.
Mogg Fanatic was the first and is a good. What's good is that you can sacrifice it and deal one damage directly to a opponent. You can block a creature and sacrifice it in response and deal 1 damage in the face or maybe kill another creature that's been blocked or not.
Now I usually don't play Mogg Fanatic but often Fanatical Firebrand. The differences is Fanatical Firebrand have haste. That means i can attack with him the first turn i play him with's is in portent. We are a aggressive and can we deal more damage faster we need to take that chance. Now you can tap it and sacrifice it, to deal one damage to anything. Which is a down grade, but the haste makes up for it.
Often when you want to use the sacrifice ability you don't attack which is a sign for you're opponent. But often they need to block an if they don't you can steal tap, sacrifice and deal the damage if it is necessary. Often it is not.

Then we come to the odd boll Goblin Arsonist, It doesn't have haste and you can't sacrifice it to deal the damage so do we need it? Well that's what Mogg Fanatic or Fanatical Firebrand can do good. But what Goblin Arsonist is better at is killing things. You can block with Goblin Arsonist and kill a one 2 toughness creature or two 1 toughness creature's. You can attack and sacrifice it to Goblin Grenade and deal one extra damage while Mogg Fanatic and Fanatical Firebrand need to be sacrificed by there own ability for the one damage to work.
So which do i take and that is more for you to deside. Some people like Mogg Fanatic some Fanatical Firebrand and few play with Goblin Arsonist. It's more about what you're play style prefers and by testing them you will know what you like.
It's good too see the strength and weaknesses of these three and important to try them out you're self.

(So it comes with some fun perks and if you have gained first strike from Legion Loyalist you can deal first strike damage then sacrifice Mogg Fanatic and deal a additional 1 damage before normal combat damge.)

Damping Sphere:

Damping Sphere is god to slow down combo decks while you often still can do much to damage and play goblins with out that much of a draw back.The ability that turn tron lands in too wastes is less useful. Becouse against tron you often win before that point or will win.

Goblin Chainwhirler and the Forked Bolt:

Forked Bolt is a Goblin Arsonist on a spell put Goblin Chainwhirler is a bigger and often much harder treat. in combination with a later whacker it shows much potential to get you beck in to the battle. There is the problem of getting one in to the starting hand or top when you don't have enough lands to play it. Put against midranged, token and decks with small creatures it can often do more then the Forked bolt. The Forked Bolt is often very situational and if you get a Forked Bolt you rather won't a Lightning Bolt or Goblin Grenade for the maximum or fatal damage. Forked Bolt works but i feel there are better options.

Look at:

Mtg goldfish uppdated 8-whack deck.
https://www.mtggoldfish.com/archetype/modern-8-whack-63570#paper

My Gruul version.
https://deckstats.net/decks/96117/1586090-8-whacky-command-s/en

My Boros version.
https://deckstats.net/decks/96117/1586261-whacky-boros/en