M I R A R I   F I R E   J E S K A I 

A semi-spicy Fight with Fire / Banefire + The Mirari Conjecture control/combo deck originally tailored for Bo1, tweaked for Bo3.

Tested in Constructed Event Bo1 and Bo3 with strong performance, especially against aggro and midrange decks.
Please note that this deck uses a fairly typical Jeskai framework and does not always require you to combo off in order to win.  Oftentimes, a well-protected Niv-Mizzet or a Fight with Fire copied with Expansion will ensure victory.

This list started off as a Bo1 list, but I have adapted the mainboard and sideboard to make the deck viable in Bo3.

Started playing this deck again in Bo1 constructed event, shortly after RNA release, so I decided to keep a record of my progress.

 MTG ARENA CONSTRUCTED EVENT LOG (BO1) 

04/02/2019 - 7-2 run - CE 7-2 ICRs
01/02/2019 - 7-1 run - CE 7-1 ICRs
31/01/2019 - 7-2 run - CE 7-2 ICRs
31/01/2019 - 7-2 run - CE 7-2 ICRs
28/01/2019 - 7-1 run - CE 7-1 ICRs
27/01/2019 - 7-2 run - CE 7-2 ICRs
23/01/2019 - 7-2 run - CE 7-2 ICRs

 BO1 AND BO3 MAINDECK CHANGES 

BO1
OUT - 4x Opt.  IN - 4x Revitalize.  After having played in the Bo1 Constructed Event queue and ranked ladder with 4x Revitalize in place of Opt, I've decided that Revitalize performs exceptionally well due to how many aggro and burn decks are found in these environments.

 MATCHUPS AND SIDEBOARDING 

MONO RED AGGRO  /  MONO RED BURN  /  RAKDOS BURN
OUT - 1x Niv-Mizzet, Parun and 1x Cleansing Nova.  IN - 2x Lyra Dawnbringer.  Lyra's First Strike coupled with Lifelink will make a major difference in this particular matchup where and Niv can be killed by burn during or before combat.  Nova is, unfortunately, far too slow here, but having a one of going into mid game can help stabalize.

GOLGARI MIDRANGE / SULTAI MIDRANGE
OUT - 1x Niv-Mizzet, Parun, 1x Expansion // Explosion, 2x Seal Away, and 3x Syncopate.  IN - 3x Disdainful Stroke 3x Ixalan's Binding, and 1x Mass Manipulation.  Niv is less useful here due to the ridiculous amounts of removal that usually gets run in Golgari and Sultai decks.  Bindings can be amazing when properly protected.  Stroke answers most of the major threats in this match up in the mid to late game, and Manipulation can completely close out games by taking control of key creatures and Planeswalkers.

NEXUS
OUT - 4x Deafening Clarion, 2x Seal Away, and 1x Settle the Wreckage.  IN - 2x Devious Cover-Up, 2x Ixalan's Binding and 3x Disdainful Stroke.  Clarion, Seal, and Settle are all dead cards here.  Cover-Up helps you recur your counterspells infinitely as long as your opponent isn't running graveyard disruption.  Binding is useful for locking the opponent out of an array of problematic permanents, and Syncopate is very useful for exiling Nexus of Fate and Chemister's Insight.  Stroke also seems useful as Nexus decks often run an array of expensive spells.

GATES
OUT - 4x Deafening Clarion.  IN - 3x Ixalan's Binding, and 1x Settle the Wreckage.  Clarion is about as dead as it gets in this matchup.  Binding is useful for locking the opponent out of an array of problematic permanents such as Gatekeeper Ram and Gate Colossus.  Settle also comes in useful and prevents recursion of Colossus.
NOTES - Syncopate can actually become fairly difficult to utilize in this matchup due to how fast Gates usually accelerates ahead in mana if allowed to.  It may be beneficial to replace them with Disdainful Stroke.

WHITE WEENIE / BOROS WEENIE / ESPER HERO / MARDU AGGRO / X TOKENS
OUT - 2x Banefire.  IN - 2x Lyra Dawnbringer.  Lyra's First Strike coupled with Lifelink helps with holding back the board until you can draw into a board wipe or stabalize with counterspells.

DRAKES  /  ARCLIGHT PHOENIX  /  NIV-MIZZET
OUT - 4x Deafening Clarion and 1x Settle the Wreckage.  IN - 2x Lyra Dawnbringer and 3x Ixalan's Binding.  All creatures in Drakes decks, save for vanilla Pteramander, are out of range of Clarion, so it often ends up being a dead card unless you can cast double Clarion, which is very inefficient on mana.  Lyra reliably blocks Drakes and Niv-Mizzet, Parun with First Strike and gains you life.  Drakes decks often have no answers to enchantments, so Bindings and even Seal Away can be very useful in shutting them down.

ESPER CONTROL / JESKAI CONTROL / MARDU CONTROL / CHROMATIC BLACK
OUT - 4x Deafening Clarion, 2x Seal Away, and 1x Settle the Wreckage.  IN - 3x Legion Warboss and 3x Disdainful Stroke.  Clarion is basically a dead card in the control mirror.  Warboss will help add early pressure and Stroke helps combat spells in the mid to late game. 

 NOTES AND CONCERNS 

02/02/2019 - Sideboard completely reworked.  Matchup notes have been changed to properly match the changes.
27/01/2019 - Tried Constructed Event and Bo1 Ranked Ladder with 4x Revitalize added in place of 4x Opt because of the abundance of mono red decks in these particular queues.  Results were overwhelmingly positive.
26/01/2019 - Updated deck to suit Bo3 as sideboard has been rehashed and tested.  Core build could probably use some updates but will require further testing.
22/01/2019 - Been playing this deck again quite a bit recently.  Haven't managed any flawless runs, but pretty much always profits in gold in Constructed Event.  Deck has been performing very strongly vs any variation of mono red and Rakdos burn.  The addition of Absorb into standard has been a godsend.
12/01/2019 - Won another long game vs a Golgari deck in Diamond 1 of the MTGA ladder.  Player seemed to be spec'd to beat control, main decking 4x Midnight Reaper and various other anti-control cards.  Player was able to build up to 42 life due to my deck's inability to deal meaningful damage throughout the game.  I was not successful in protecting Teferi, Hero of Dominaria due to having lost control of the board, and lost my third one due to a mistake in tapping out and losing it to Vraska's Contempt. Hard casting Niv into a Ravenous Chupacabra or The Eldest Reborn seemed futile without counters in hand.  Was able to stretch the game out long enough until the opponent had 10 cards in their deck (opponent had been aggressively Surveiling with Doom Whisperer and drawing a lot of cards from Midnight Reaper's triggered effect).  Casted Explosion for 10 on opponent and targetting them with the card draw portion, causing him to draw his last 10 cards, which left them with no options but to concede.  Winning with 2 life left always feels extra satisfying.
11/01/2019 - Won an incredibly long and arduous game against mono red aggro in the 7th game of Constructed Event.  Player got to play 3x Experimental Frenzy and had a stacked hand throughout the whole game as a result of me not being able to take damage from Risk Factor.  All three Seal Away was used to good effect, and 3x Revitalize ensured survival.  Went into late game with 2 health, Teferi, Hero of Dominaria and Search for Azcanta // Azcanta, the Sunken Ruin developed, and a couple of counterspells in hand.  Managed to win with the third step of The Mirari Conjecture and Kicked Fight with Fire.  Both Deafening Clarion and Cleansing Nova came in useful, but did find that I had a spare of each in hand towards the end of the game.  More counterspells in the main deck might be necessary, but I'm not sure what I would cut.
11/01/2019 - Achieved hot streak in constructed event vs a mix of aggro and control decks.  Seal Away proved incredibly useful, oftentimes finding full usage of all three copies.  May still require more counterspells in order to properly combat control.

 CHANGELOG 

02/02/2019 - Removed 1x Crackling Drake.  Added 1x Expansion//Explosion.  Crackling felt far too underwhelming in too many matchups.  With the abundance of Esper Control in Bo3, an additional Expansion feels like a strong addition.
01/02/2019 - Removed 1x Detection Tower.  Added 1x Clifftop Retreat.  Tower has been seeing very little use lately.  May revert this change if I suddenly start to see an increase in the presence of Carnage Tyrant, Drakes, or mono blue shenanigans.  Clifftop retreat has been added to help with the consistency of turn 3 Deafening Clarion and turn 5 Cleansin Nova.
31/01/2019 - Reverted the change from 3x Absorb to 3x Sinister Sabotage.  After much testing and deliberating, I've come to the conclusion that Absorb is far more useful on average compared to Sabotage.
28/01/2019 - Removed 3x Absorb.  Added 3x Sinister Sabotage.  This change was made to help with consistency in Bo3 matches.  I would still recommend running 3x Absorb if playing Bo1 due to the abundance of aggro and burn decks in that particular queue.
27/01/2019 - Removed 1x Absorb.  Added 1x Spell Pierce.  After losing a number of counterspell wars, I realize that a one of Pierce can literally win games.  Multiple copies of Absorb often weren't always useful, whereas a single Pierce could have helped push the advantage.
27/01/2019 - Removed 1x Search for Azcanta // Azcanta, the Sunken Ruin.  Added 1x Banefire.  Early Azcanta often made it difficult to contest aggro in the early turns, and drawing two of them early on often proved quite detrimental.  Considering making space for one in the sideboard.  An additional Banefire felt much-needed as an answer for Planeswalkers that the deck does not have outside of Expansion // Explosion and counterspells.
25/01/2019 - Removed 1x Syncopate.  Added 1x Glacial Fortress.  Slight manabase tweak to improve consistency and help avoid mana screw.  While Syncopate is a good card, having so many in the hand is often not optimal.
24/01/2019 - Manabase tweaked.  Added 4x Hallowed Fountain.  Removed 3x Island and 1x Glacial Fortress.  This changed happened during RNA release, but I forgot to log it.  Manabase seems to function well with 3 of each check-land.
23/01/2019 - Removed 4x Revitalize.  Added 4x Syncopate.  Decided to try out a full playset of Syncopate in an effort to combat Nexus of Fate decks and the control mirror.  Has been producing favorable results so far, even against mono red. 
23/01/2019 - Removed 1x Deafening Clarion, and 1x Cleansing Nova.  Added 1x Absorb, and 1x Banefire.  The loss of a Clarion might significantly affect the deck's ability to combat aggro decks that go wide fast, but it really seems like not running 4x Absorb in this mono red BO1 meta is a bit of a mistake.  The inclusion along with Banefire should significantly help the control mirror as well.
22/01/2019 - Removed 1x Enigma Drake.  Added 1x Crackling Drake.  Most people argue that Enigma's low  and less strict mana cost is enough to run it over Crackling, which is a fair point, but the creature being in range of Ritual of Soot is crippling, and having to use a counterspell to save the drake is a pretty big setback.  Decided to switch to a single Crackling and do further testing.
20/01/2019 - Removed 1x Seal Away.  Added 1x Enigma Drake.  Deck was sorely in need of an alternate and relevant win condition, and Enigma seemed like a good fit.  The removal of Seal hopefully will not hurt too much against aggro.
20/01/2019 - Removed 1x Spell Pierce and 4x Sinister Sabotage.  Added 1x Banefire, 3x Absorb, and 1x Niv-Mizzet, Parun.  Pierce only seemed to perform optimally in the control matchup, and would too often end up being a dead card.  Having a single Banefire in the deck can often help against the control mirror when the opponent is at a moderate life total and holding up counterspells.  Absorb is a strong counterspell for the same cost as Sabotage that should greatly help with surviving mono red which is fairly popular in the current BO1 meta.  Niv is almost always useful when you can cast him and protect him, and having only one in the deck seemed unsubstantial.

 COUNTERSPELLS : 

 ANTI-AGGRO // ANTI-BURN : 

 ANTI-CONTROL : 

 REMOVAL : 

 CARD DRAW : 

 ALTERNATE WIN CONDITIONS :