Sideboarding: (THIS DESCRIPTION IS STILL IN PROGRESS)

Against Mono Red:

Threats: Small creatures, dmg spells, Menace, life gain block.

IN: 2x Kalitas, 3x Aether Gust, 1x Shadow's Verdict (If enemy is heavy in creatures with cmc <=3)

OUT: 2x Narset, 1x Commit, Grasp, Dig Through Time

Tactic: Destroy all threats which enters board. Counter only noncreatures which threats more than 2-3 direct damage or big creatures (Hazoret, Glorybringer etc. For noncreatures: Walkers, Red Leyline). Sorin / Kalitases grant you extra life so don't throw them on the table without securing them.

Against Niv to Light:

Threats: Bring to Light / Niv Mizzet on turn 4, Valki, Omnath, Klothys.

IN: 2x Test of Talents, 1x Go Blank, 1x Thought Distortion, 2x Aether Gust

OUT: 4x Fatal Push, 2x Censor (on loss) / 1x Censor + 1x Narset (on win)

Tactic: You are against deck which from turn 4 can basically refill whole hand with the toolbox cards. On first game you must block his Bring to Llight / Niv Mizzet from resolving, or pray he won't get card advantage. Besides Niv Mizzet, most common threats are Valki (1 or 2), Omnath and eventually Klothys. He have walker removal, multicolor removal, Slaughter Games - only counter spells he have are Disputes. What to do: Fields of Ruin into the color he lacks, so Niv/Bring cannot be casted. Counterspells only on Threats, no sense in countering Iteration, Dreadbore Caryatid - unless, we're on "topdeck" mode, and try to draw better.

After Sideboarding, take note, that he will put Disputes in. Test of talents should target exclusively: Bring to Light and Disputes. Go blank should be played in before he will Bring / Niv, even on turn 3, maybe you'll get rid of lands he will be needing. Thought Distortion is for the moment when he refills his hand with Niv Mizzet - It will basically crush his advantage. Aether Gust is for slowing the game. Do not attempt it early on - slowing down player who has lands in hand does not work great. It is better to slow him with big spell, so you can have more mana for counter, or time to Dig for answers. Besides Niv Mizzet, you should be able to win with big sharks attack as he has no other fliers. Extra note - If you notice Coma - keep all Exiles effect you have on the serpent.

Against JUND:

Threats: Korvold, Bolas's Citadel, Mayhem Devil.

IN: 3x Aether Gust, 2x Kalitas, 1x Shadow's Verdict, (eventually: 1x Go blank)

OUT: 2x Narset, 1x Commit, 2x Censor, 1x Push (?), 1-2 Dig Through time(?)

Tactic: Take note that only TWO noncreature spells are in opps deck: Citadel and Company. Beside creating a wide board opponent want to finish the game with Korvold or Shooting with Mayhem Devil (most of the time). To fight with him you'll need to cast verdict on his wide board, counter Korvold/Citadel. Cage will slow him down, as he will look for Binding of the Old Gods or Thrashing Brontodon. Fatal push's are for Priest of Forgotten Gods, so he will not force you into discarding. Using Pushes early on on mana Dorks is only good when you are surely countering his bigger thingts on turns 3 and 4. Kepp counting his mana. with 5 he can put in Korvold and on 6 citadel - keep that in mind when you have only 1 counterspell left in hand.

Against RAKDOS AGGRO:

Threats: Young Pyromancer, Kroxa, Dreadhorde Arcanist, Lurrus

IN: Shadow's Verdict, 2x Kalitas, 1x Go blank

OUT: Heartless Act, 2x Narset, 1x Commit, Censor (?)

Tactic: It is basically mono red with discard shenanigans. After successfully casting Verdict Opp should just concede. You'll most likely be Thoughtseized few times, so it is best to Fatal Push Arcanist, and try to draw into Verdict on End Step of Turn 4, so you can cast it. We pull out 2 removals, as his creatures are only cmc2, fatal pushes and thirst will be enough to slow down game to the state where you can cast verdict of blank his hand and graveyard. Kalitas is shining here. Opp will most likely side out pushes, so Kalitas will probably live on for a bigger part of the game. Lurrus is not a BIG threat as he will most likely be cast after yout Verdict / Blank, so it will be a 3/2 lifelink cat for most of the times. Be mindful of Thoughteizes - with Kolaghan's commands those are spells you will most likely want to counter. Rest are just targets for your removal. Also - if he uses manlands, Destroy them with Fields.

Against Spirit Aggro:

Threats: Spell Queller, Skyclave Apparition, Spirit Lords (those with +1/+1 effects)

IN: 2x Mystical Dispute, 2x Kalitas, 1x Shadows Verdict

OUT: 1-2x Dig, 1x Commit, 1x Heartless act, 1x Baleful Mastery

Tactic: Besided opponent puting in Disputes after side, you are playing against 30+ Creatures with flying and cmc 1-3. You are playnig for Event / Verdict. Removal is basically only for creatures which pumps other spirits. He will race you, there is no end-game for spirits. He might drag the game by putting 1-2 creatures and ping you with some damage and wait for company to be casted at EOT step, but it is still just a race. After sideboard, the only cards you care for are: Verdict, Kalitas, Event, some counters. And from Opp side you need to take out: Apparition (he exiles Kalitas) Dispute and Spell Queller. Also take note that a big Shark can slow the game and give you a big advantage. And when opp is going for longer race by pinging you with small creatures and waiting for Company - you also drag the game untill you can put Sharknado hardcasted and have some spells ready.

Against Izzet Aggro:

Threats: Arclight Phoenix, Crackling Drage, Thing in the Ice, Demilich.

IN: 1x Go Blank, 1x Thought Distortion, 2x Mystical Dispute, 2x Aether gust, 1x Kalitas (?)
OUT: 1x Infernal Grasp, 1x Bloodchief Thirst, 1x Laguish, 1x Dig Through time, (?)

Tactic: Opponent is counting on casting few spells in a round so he can revive Phoenixes or flip The Thing. The latter is a great target for Fatal Push and Phoenix must be exiled. As we do not count on Verdict (It exiles cmc <=3, so misses Phoenix) we need a Kalitas / Go Blank solution. Opponent does not run much counter spells, so we should be able to force him into using one or two, before we wipe his board with event od put kalitas + removal. Go blank is the best card we can play against Izzet Aggro, as it takes out potentially two spells and clears his grave from delving into Treasure Cruise / reviving Phoenixes. Thought Distortion is a fine addition, and if casted with Fliers in grave, you are most likely winning - he won't be able to cast 3 spells a turn (or maybe he will draw like crazy - not much we can do with that)

Against MIRROR:

Threats: Sharknado, Gearhulk, Ashiok

IN: 1x Go Blank, 1x Thought distortion, 2x Mystical Dispute

OUT: 4x Fatal Push, 2x Shadows' Verdict

Tactic: Basically the worst matchup. If you can setup Narset + Memory, you will gain advantage which will most likely win you a game. In other cases, you try to outcounter your opponent and hardcast Sharknado so you can have threats on board. After sideboarding, you are focusing on securing your discard spells (Go Blank to be exact, as Distortion cannot be countered) and keep in mind that Disputes are for his blue Threats - Gearhulk, Sharknado, Ashiok - all blue.