Mulligans
General Mulligans
Fire Fly and Mana Wyrm are always keeps, they provide so much in the early game because of their health-pools in combination with the upgraded Mage hero power.
If you have either Fire Fly or Mana Wyrm guaranteed in your opening hand, Black Cat and Kirin Tor Mage are viable to keep in your opening hand as well. Black Cat is a solid stat-line on T3 and always draws a card. While Kirin Tor Mage can be a huge tempo play if you manage to find a secret by T3, less so if you don't.
Aggro Mulligans
Fire Fly and Mana Wyrm are always keeps, because board control wins the game more often than not, and your hero power isn't as effective against token style decks like Odd-Paladin or Token Druid.
Tar Creeper can help to solidify your board lead against other aggressive decks if you can build a board of some kind by T3.
If you fall behind on board to decks like Odd Paladin or Token Druid, Arcane Missiles and Cinderstorm can shutdown a Level Up or provide a small comeback mechanic.
If you're playing against a lot of Aggro decks, you can cut one Nightmare Amalgam or one Arcane Intellect for a second Cinderstorm.
Control Mulligans
If you have either Fire Fly or Mana Wyrm guaranteed in your opening hand, Black Cat is a solid stat-line on T3 and always draws a card. While Kirin Tor Mage can be a huge tempo play if you manage to find a secret by T3, less so if you don't.
Against Control decks your hero power is much less useful in the early game, and if possible you should spend your mana chaining your elementals and building the board. Once the Control decks get ahead on board, you've basically lost unless you can get REALLY good value out of Blazecaller and Fungalmancer.
If you're running into a lot of Control decks, you can cut the Arcane Missiles for a second Cinderstorm and second Nightmare Amalgam for a little more midrange pressure.
How It Works...
Unfortunately, playing Baku The Mooneater and odd-cost cards only, means that you don’t have access to Mage’s even-cost burn spells like Frostbolt and Fireball. However, we get our 2 damage Fireblast hero power, and that pushes the deck to be more board-centric where the hero power can have tangible value, rather than a normal Tempo Mage style deck where it just cleans up after cheap spells.
This deck uses the early game control potential of 1 mana minions, in combination with the 2 damage Mage hero power, to progress into the midgame with a headstart on board.
On turn 3 this deck uses powerful 3 mana minions like Kirin Tor Mage with a secret or Tar Creeper to maintain the board presence from the early game long enough to reach turn 5.
Landing a Fungalmancer on 2 minions on 5 can win some games right there against other aggressive decks, and the tempo of Bonfire Elemental with an activator can provide enough steam to beat some control decks.
The deck also has Frost Lich Jaina to help extend the heavier end of this deck and can play a slower value game if needed against more aggressive decks with two Blazecallers and Baku the Mooneater, but will often lose against Big Spell Mage or other value/control oriented matchups.
Considerations for Changes
If you’re playing against Aggro decks you can cut Arcane Intellect for another Cinderstorm.
If you’re playing against Control decks you can cut Arcane Missiles for a second Cinderstorm and Nightmare Amalgam.
I’ve been experimenting with this, +1 Mirror Images, -1 Cinderstorm — seems alright, not sure which is more optimal yet.