There are a lot of powerful Goblin tribal creatures legal in Pioneer, but we think that the best way to build a deck featuring this tribe is to focus on a token swarm strategy that looks to go under the opponent's strategy.
Goblins Decklist (Pioneer)
4 Foundry Street Denizen 4 Legion Loyalist 4 Fanatical Firebrand 4 Goblin Instigator 4 Dragon Fodder 4 Reckless Bushwhacker 4 Hordeling Outburst 4 Cavalcade of Calamity 4 Stoke the Flames 1 Wild Slash 4 Dynacharge 3 Castle Embereth 16 Mountain (343) 2 Goblin Trashmaster 4 Goblin Chainwhirler 1 Goblin Rabblemaster 1 Goblin Ringleader 1 Legion Warboss 1 Vandalblast 1 Pithing Needle 4 Rending Volley
This deck is technically more of a tokens decks than a Goblin tribal deck, it just happens to feature a lot of goblins since a lot of the best cheap token strategies in mono red are goblins. Foundry Street Denizen is one of the best payoffs for going wide, as we can often get 3 or 4 damage per turn out of our 1-drop. Hordeling Outburst, Dragon Fodder, and Goblin Instigator give us a ton of redundancy on the token effect.
Stoke the Flames is a great reason to build your mono red deck as a swarm deck. The 1-drop burn spell options are much more limited in Pioneer than in Modern, so it can be a bit harder for red to deal with larger creatures such as Felidar Guardian or Thing in the Ice. Stoke the Flames is extremely easy to cast with all of our token cards, and we can even sometimes play it for free while further developing our board in the early turns. To have this tempo play as an option is incredible from a card that gives us quite a lot of reach for burning out our oppoonent.
Reckless Bushwhacker is the best payoff for the token strategy, being able to turn even a mediocre board into something the opponent has to respect. Dynacharge is more powerful pump spell in this color from a mana perspective, but it does require our board to be well established before it can do anything. However, many opponents will not be prepared for the instant speed pump and will either find themselves having made horrible blocks or simply dying before they expected.
Cavalcade of Calamity does seem like a natural fit for a deck that loves to produce a bunch of 1/1 creatures already, though it can have its awkward moments. It doesn't work great with Reckless Bushwhacker or any other sorcery speed pump spells we may want to play, though this downside is minimal compared to its raw power level. It gives us much more reach for opponents who are able to assemble blockers, and is often just impossible to stop if we are able to draw multiple copies.
Castle Embereth pretty much has the same exact text as some of the payoff spells that we're already running, so it's an obvious and huge inclusion for this deck. The opportunity cost is very low in a deck that can just run a bunch of Mountains, and it drastically increases the consistency with which we can turn our tokens into real threats.
There are plenty of powerful goblins in Pioneer to consider, so if we ever find ourselves in a world where we don't expect much targeted removal we can play some of the more powerful but slower goblins. Some of them are still very potent sideboard options to consider against opponents who are either weak to a specific type of ability such as Goblin Chainwhirler or who would be effective at blocking a swarm of token creatures such that we need to increase our power level.
That's the deck! It's worth noting that this deck is very easy to build on a budget. We didn't intend for this when brewing it, which means it was built for power level alone, but that could make it a good deck to try to get started in the format!