Earthen Ring Farseer (1-2)
Counterspell (1)
Polymorph (1)
Sen'jin Shieldmasta (1)
Faceless Manipulator (1)
The Black Knight
Ragnaros the Firelord
Alexstrasza
Ysera
Pyroblast (1)
Cairne Bloodhoof
Harrison Jones
Acidic Swamp Ooze (1)
Arcane Intellect (1)
Twilight Drake (1-2)
Big Game Hunter (1)
Spellbreaker (1)
Ironbeak Owl (1)
Flamestrike (1)
Abomination (1-2)

Q: Too little card draw?
A: No. This deck cycles well and you will quickly overdraw after using Duplicate + draw engine. If you desperately want more draw, add one Arcane Intellect as suggested above. 

Q: I think some of your choices suck, can i replace X with Y?
A: Yes. Any Card I recommend for a swap is listed in the Section above.

Q: This deck seems slow, sucks vs aggro?!
A: I heared that quite often and its not exactly true. Im sorry to say that but playing mage is different from any other control Deck and you are more likely just unexperienced with it, besides it is "harder" to play than control Warrior. Even though i have to admit that this deck is not made as an aggro counter so you will have to make some changes if you want to build it like that. Be aware that it will hurt your control Matchup. The changes i do recommend are listed below in the specific Matchup section and will include most likely changes for Zoo (ofc suggestions for others), because against other aggro decks changes are not necessarily needed.

Q: How can i replace Alexstrasza?
A: I do not recommend replacing her because you can use her so fine for a heal against aggro decks. If you dont need her for that, i would suggest Pyroblast for the offensive nature.

Q: Is it possible to swap core cards?
A: Yes but i would be careful with that. One thing i can suggest : replace  Kirin Tor Mage for a Spellbreaker

Q: Suggestions if facing a lot of Handlocks?
A: Big Game Hunter (1)

Q: Suggestions against Zoo?
A: Abomination, Zombie Chow

General rules against aggro : Try to mulligan for Mad Scientist, Earthen Ring Farseer, Frostbolt, Unstable Ghoul, than Sen'jin Shieldmasta and Acolyte of Pain. You want to draw into your Sludge Belcher, aswell as Flamestrike. It is important to understand that aggro Matchups are more a Battle for the Board and Life as for Resources, because its very likely that aggro Decks are running out of steam very quick (zoo loses his life). Therefore aggro Decks wont trade if they dont absolutely have to and that is the Key, you have to force them to do that and that is the Reason why taunted Minions are so good. Aggro Decks tend to establish a large board and taunt Minons force them to downsize it. Also you can see now why AOE is so good against aggro and why Unstable Ghoul and Earthen Ring Farseer are Keycards. Besides their body Ghoul is a taunted Minion which also provides AOE, while Earthen Ring gives you health. The Water Elemental on the other hand can keep weapon classes off your face and if your facing a lot of Weapon Classes, consider putting in Ooze is maybe worth it.

General rules against control : Mulligan for Mad Scientist, Water Elemental, Kirin Tor Mage, Frostbolt. One of my friends found fitting words for the key in control Matchups "once you can duplicate your 4+ Minions its gg anyway." If you get the combo Unstable Ghoul + Acolyte of Pain keep it. While control Matchups are much more complex than aggro, their general understanding is as simple as aggro. Its just the opposite, control Matchups are a Battle for Ressources first, than Board and after that Life. It constitutes the Reason why Duplicate is the Key Card in control vs. control, especially in combination with Sylvanas Windrunner. She alone is a Card which forces your opponent get a answer as she not just destroys his Ressources but steals them for you at best. Duplicate doubles that effect on her and on any other good Minion (Ragnaros the Firelord just for expample) in control Matchups which you now can hopefully understand a bit better.

Mulligan agressive for Unstable Ghoul, Earthen Ring Farseer, Mad Scientist, Frostbolt. Water Elemental and Acolyte of Pain are also a good keep. Every hunter will try to face you down as quickly as possible and therefore you have, as might noticed plenty of answers in this deck to stall their agression. Ghouls are very strong in this Matchups as they will rape Huffer, Haunted Creeper, Leper Gnome, Mad Scientist and Webspinner. Sometimes everyone at the same time.
Frostbolting Undertaker is a good play, otherwise save it for Houndmaster. Polymorph will take care of the Savannah Highmane and if you dont have it, use Fireball.
Dont be afraid of the Eaglehorn Bow, because once if you have a living Water Elemental, he wont be able to use it and its much more safe to activate his traps and even if your Elemtal dies, it will stall 6 Damage.
Counterspell is able to crush his Kill Command and your Farseer will keep you alive and also represent a solid body for the board. Acolyte of Pain seems weak but its likely that they will kill him also as soon as possible to denie you from drawing answers. Both is good for you!
Things you want to get duplicated : Ghoul,Farseer,Senjin, Belchers, Water Ele. Once you can duplicate one of them the Matchup gets highly in your favour Just watch out for a Flare but nowadays many of them only run 1 or even zero.

Keep : Frostbolt, Earthen Ring Farseer, Mad Scientist, Kirin Tor Mage, Fireball, Water Elemental.
Duplicate : Water Elemental, Sludge Belcher, Loatheb, Sylvanas Windrunner and any other 4+ Drop.

Frostbolting the Northshire Cleric is fine alswell as using it on a turn 3 Blademaster without Circle of Healing. Kirin Tor Mage is excellent here because of the 4 Attack and overall this Matchup is really ok. Priests will have a very hard time to deal with a duplicated 4+ drop and Flamestrike will almost certain kill all oh his Minions. Try to ping his minions over face unless he has Cleric in play, that implies you have Flamestrike ready and make him fear a boardclear even if you dont have it, it will make your trades easier for you. Counterspell is a very powerful tool because unless he has a Power Word: Shield or Coin it will hurt him very much to remove it. This is also why a duplicated Loatheb can seal the game right away. I cant really say much more here because fighting Priests is just a slow grind and you will do fine if your Duplicate does its Job. Just make Sure he cant Cabal Shadow Priest your Acolyte of Pain, Unstable Ghoul and Mad Scientist and not to get caught by Mind Control.

Keep : Water Elemental, Mad Scientist, Kirin Tor Mage, Frostbolt, Earthen Ring Farseer, Acolyte of Pain
Duplicate : Water Elemental, Sylvanas Windrunner and your other 4+ drops (but Senjin)
Your goal : Denie his card draw and give him as little armor as possible.

How to do? Use Frostbolt on Acolyte when he is not already activated by Cruel Taskmaster. Try to maximum two hit a Armorsmith. Avoid playing your unstable gouls against his Armorsmith or Acolyte unless you hold a Frostbolt or have something on board which will deal with them right away. DO NOT play a duplicated Sylvanas Windrunner or other Legendarys if he hasnt already played his Brawl. Using Fireball for Baron Geddon or leftovers of Grommash Hellscream is a really good move, also you will try to save your Polymorph for his Ysera if he runs her. Always value Polymorph over Fireball. Once you can establish a good board and maybe duplicate your Water Elemental he will be forced to Brawl or use his hard removal on "just" a 4 drop which will lead in a huge advantage for you in the lategame.

First note : If you facing a lot of Zoo, make some changes or this will be a bad Matchup. Change for example Sen'jin Shieldmasta and one Counterspell for two Abomination.
Keep : Frostbolt, Unstable Ghoul, Mad Scientist, Sen'jin Shieldmasta
Duplicate : Unstable Ghoul, Abomination, Sen'jin Shieldmasta , Sludge Belcher
Your goal : Grind him out of Steam if possible

How to do? Make sure that your mulligan is agressive and hope for the best. Frostbolt his Undertaker, Knife Juggler, Flame Imp. Fireball his Doomguard, Dark Iron Dwarf, Nerubian and Flamestrike his board when possible. Even though this battle is almost entirely for Board and Life, you have sometimes to play it slow to make best use of your Hero Power. Even if it seems that this play can hurt you a bit more, but if that increases your chance of a great Duplicate it is often worth it. Use Alexstrasza for heal on yourself. Nothing more to say.