I'm a regular legend player and just leveled from Diamond 5 to Legend with this deck in a day (23 wins to 8 losses).
I didn't struggle in any matchup, but the deck is quite tricky to play correctly with all the comboing and reductions, etc.. . Warrior can be somewhat problematic but you basically set up for a big potion of illusion + raz or some other high damage combo using a maylgos spell and lots of spell damage.
20 upvotes and I will write and in-depth guide for you guys.
As promised, here is the guide. I will do mulligan and then each individual matchup. My current stats with the deck are 51 wins to 23 losses in Legend.
In most matchups you are basically doing a mulligan for 2 specific cards.
Imprisoned Phoenix and Cram Session. With those two cards in your opening hand, you are effectively guaranteed to draw 3 cards on turn 3 (if you coining phoenix, which I would always suggest) or turn 4 at the latest. Other decent cards in your opening hand are Violet Spellwing or Arcane Missiles specifically against aggro decks such as Hunter or Rogue, against slower decks I would always mulligan for phoenix and cram session though.
So far I've won almost every match against warrior. Try to generate as many damage cards as possible with your discover cards and do not overplay your spell damage minions early on, because warrior has a lot of removal. The goal should be to keep their armor somewhat low (but don't overextend) and then set up for a big spell damage turn with Potion of Illusion. If you ever feel like your opponent is out of range due to having too much armor, try to discover lategame cards. With Azure Explorer try to get a Ysera or Dragonqueen Alexstrasza and just play for value.
I don't think I have played a single shaman actually lol. But I don't think the matchup should be terribly difficult. Just set up for a big spell damage boost and draw, draw, draw...
Against Rogue, assuming it is aggro rogue, you definitely need removal early on. I still suggest keeping Phoenix and Cram Session but I would also suggest you keep Arcane Missiles and Violet Spellwing. Boosting your arcane missles with any spell damage early on is very powerful against all their 1 health minions.
This is the most difficult matchup I found. It is not completely unwinnable, but if they have a strong curve it is very hard. Try to draw as much as possible in the first 4 turns, so by then you can remove some of their bigger stuff. You can actually use your arcane missiles and other removal spells against their minions because you are likely not going to win by hitting face. Try to buy time and then in the endgame play for value, discover strong dragons and valuable spells. Eventually they can run out of gas, but this matchup is definitely a coin-flip. It really depends on the draw and the discover-options you get.
So far I have won almost every single game vs. hunter. Arcane missiles is incredibly powerful as removal and you can have big board swing turns at around turn 4 or 5. It's ok if you take some damage in the first 3 turns, just try to draw and set up your removal by then. I mostly stabilized against hunter at around 15 health and then you just destroy them.
I think I've only played 2 druids so far and the matchup seemed pretty easy. Use the first 5-6 turns to draw as much as possible and then unleash all your spell powered damage spells at around turn 7 or 8. Druid is very slow, so you can just play your spell damage minions without being too worried about them getting removed.
It's actually quite similar to the druid matchup. You can absolutely use the first 5 or so turns to just draw and play your minions, draw some of their removal and set up for a big damage turn later on. You are under very little stress in this matchup.
Draw, draw, draw. And then unleash your damage spell once you have +3 or +4 spell damage. I really don't know what to say about this much, but in terms of discovering I would always prioritize face damage, but counter spell or any other type of secret can also be useful. With Malygos, Aspect of Magic also pick damage spells, preferably the cheapest. You don't really need board clear, because the current mage decks don't play all that many strong minions at all.
In this matchup it is important to remove all minions. Use all your removal spells on their card-generating minions such as Sethekk Veilweaver. It is very important that you don't let their card-generating get out of hand. So use all your spells as removal if need be. You can then generate more value than Priest and win a longer game. It's not a terribly difficult matchup, but priest can get out of hand if you let them generate too many cards.
This matchup can range from super easy (aggro demon hunter) to very hard (weapon demon hunter). Vs. Aggro play like you would against hunter. use your arcane missiles and spell power early on to remove their minions and then the matchup shouldn't be very difficult, because at that point it is just a weaker hunter.
if you are playing versus weapon demon hunter things can get more tricky. Use the first few turns for drawing and set up for big spell damage turns. If you ever feel like you can kill your opponent within 2 turns, do not hesitate to frostbolt their face so they cannot heal with a big weapon swing. That's your best chance to win, but the matchup did seem a little bit difficult when I played vs. those demon hunter decks.
THANKS FOR READING GUYS. If you have any more questions or feel like I should add something to the guide please let me know and I'll respond.