Introduction
This is a very aggressive deck for Pioneer, playing mostly one mana spells. The deck is built around low-CMC creatures with prowess and lots of cantrips / burn spells. The deck plays just 18 lands and only 16 creatures to be able to fit in as many spells as possible.
The game plan is to stick a few threats like Monastery Swiftspear and Soul-Scar Mage, then attack and trigger Prowess or the Young Pyromancer's ability often, while drawing lots of cards with the cantrips and killing things (or the opponent) with Shock and Wild Slash.
Unlike normal Aggro decks, this deck has lots of card draw spells, but most of them are not really cards advantage, they're just cantrips that are there to trigger Prowess.
Creatures
Monastery Swiftspear (4): The ideal onedrop. This can be a huge threat and has Haste. Nothing special, but a Swiftspear can deal lots of damage in this deck.
Soul-Scar Mage (4): The other onedrop of the deck. Doesn't have Haste, but is otherwise very similar to the Swiftspear. Its -1/-1 counter ability can come up sometimes, but is mostly irrelevant.
Young Pyromancer (4): The Pyro can create lots of tokens that are then pumped with Atarka's Command. The Pyromancer itself is very fragile and rarely attacks (only if your opponent has no blockers or when you attack all out for the win).
Dreadhorde Arcanist (4): Arcanist allows you to recast spells from the graveyard, triggering the other creatures again. The best combo of the deck is: Cast Atarka's Command, attack with Arcanist, flashback Command (that's usually 6 damage directly and +2/+2 for the team, +4/+4 for creatures with prowess).
Noncreature Spells
Crash Through (4): The better one of the one mana cantrips. Trample is more relevant than First Strike because it can push through additional damage. This card is here to trigger prowess and draw a card.
Warlord's Fury (3): A little bit worse than Crash Through, but basically the same card.
Shock (4): The basic one mana removal in red. Instant speed is nice and it can hit any target (creature, planeswalker, player). Sadly, Lightning Bolt isn't in the format and we don't play enough wizards for Wizard's Lightning, so those can't be included in the deck.
Wild Slash (4): Shock with an additional small upside. There is no reason not to play it. The "Ferocious"-part can be ignored, but having eight copies of Shock is nice.
Samut's Sprint (2): A nice roleplayer in this deck. Gives Haste, a relevant powerboost, scries and triggers prowess for just one mana. Also allows you to recast Light up the Stage with an Arcanist.
Atarka's Command (4): This card is the only reason for the greensplash and the best burnspell in Pioneer, so a deck that's focused on killing the opponent quickly is very interested in playing it. Command is a nice combo with Dreadhorde Arcanist (see above). You almost always choose modes two and four, but sometimes if your opponent has lifegain, mode one can be better.
Temur Battle Rage (1): TBR is here for the occasional surprise-kill, as our creatures can become quite large with prowess. Just a single copy though.
Light Up the Stage (4): LutS is basically a one mana spell that draws two cards. That by itself is insane and makes it nearly uncuttable. It can also trigger prowess, but it's cast postcombat most of the time because of Spectacle.
Lands
The manabase is very simple. I have playsets of Stomping Ground and Rootbound Crag for the greensplash and 10 Mountains. Just 18 lands in total, but the deck doesn't need more than 2-3 lands on the battlefield and has lots of card draw. 18 lands is actually enough to flood in most games, but you need 18 to have a good number of lands in your starting hands (two is perfect for the deck). You can actually keep some hands with just one land if you have enough card draw (i.e. a onedrop plus LutS). Copperline Gorge would be a perfect fit for this deck, but it isn't legal in Pioneer.
Sideboard Cards
Blazing Volley (3): Good against small creatures like manadorks. It can also shrink your opponent's whole board if you have a Soul-Scar Mage.
Destructive Revelry (4): Enchantment and Artifact removal that has some burn stapled to it is very desirable in this deck.
Pithing Needle (2): Needle is here to handle troublesome planeswalkers or other permanents with activated abilities. Needle is better than Sorcerous Spyglass for this deck, because every single mana counts in a deck this fast.
Blitz of the Thunder-Raptor (3): When your opponent has bigger creatures that Shock or Wild Slash can't handle, or creatures that need to be exiled, this is there for you. I'll be testing this and maybe go back to Lava Coil if i notice that i usually don't have enough cards in my graveyard.
Tormod's Crypt (3): There are many graveyard centered decks in Pioneer, and the Crypt is the perfect answer to those for this deck. Zero mana and it also triggers Prowess.
Sideboarding Guide
-will be updated-
Mono Green Planeswalkers:
Temur Reclamation:
Niv to Light:
Jund Sacrifice:
Jeskai Lukka:
Naya Winota:
Sultai Delirium:
+ In: 3 Tormod's Crypt, 3 Blitz of the Thunder-Raptor;
- Out: 3 Warlord's Fury, 3 Shock;
UW/Bant Spirits:
+ In: 3 Blitz of the Thunder-Raptor;
- Out: 1 Warlord's Fury, 2 Samut's Sprint;
UW/Esper Control:
+ In: 2 Pithing Needle;
- Out: 2 Samut's Sprint;
Mono Red Aggro/Burn:
+ In: 3 Blitz of the Thunder-Raptor;
- Out: 3 Warlord's Fury;
Mono Black Aggro and Black/Red Midrange: + In: 3 Blitz of the Thunder-Raptor;
- Out: 3 Warlord's Fury;
Green(/Black) Stompy and Gruul Aggro:
+ In: 3 Blazing Volley, 3 Blitz of the Thunder-Raptor;
- Out: 3 Shock, 3 Warlord's Fury;
Izzet Phoenix:
+ In: 3 Blitz of the Thunder-Raptor, 3 Tormod's Crypt;
- Out: 2 Samut's Sprint, 4 Shock;
Dredgeless Dredge:
+ In: 3 Blazing Volley, 3 Blitz of the Thunder-Raptor, 3 Tormod's Crypt;
- Out: 4 Shock, 2 Samut's Sprint, 3 Warlord's Fury;
Izzet Ensoul:
+ In: 4 Destructive Revelry;
- Out: 2 Shock, 2 Samut's Sprint;
Conclusion
If you want to play a blazingly fast deck that also has some reach with it's burnspells, this is the right deck for you. The individual cards aren't really powerful, but this deck preys on your opponent durdling around or stumbling a little bit.
