Hearthpwn

• If your opponent is Hunter, Mage or Paladin you should assume that he is a rush and you should keep these cards for your starting hand Arcanologist, Raven Familiar, Dragon's Fury, Tar Creeper
• versus a rush if you have the coin you should always keep it, use it at turn 4 for activating Dragon's Fury or at turn 5 some of the big 6 mana spells for board clear such as Blizzard, Meteor   
• versus a control take your time, anticipate his moves and do not rush with your removals unless you feel threatened if something goes wrong Prince Malchezaar minions are here to help, your control opponent's late game main goal will be not to let you have free Water Elemental by your Frost Lich Jaina's  hero power that is when Sindragosa's  Frozen Champions come in play by pinning them with your hero power and granting you a free Water Elemental and legendary minion in your hand
• Remember that you are not a rush but a control, your mission is to predict your opponents moves as much as you can and outlast him, defeat him on the long run
• If the opponent's minions do not threaten your hero and you have only 1 removal in your hand wait for another turn let the opponent give more value to your board removal spells
• If you got Ice Block on tend not to use the Arcane Artificer till the opponent destroys your Ice Block and try to do the combo with a spell that will clear the board and up your armor

There are 118 but because we already have 4 in our deck we will consider 114 since Prince Malchezaar cannot get you 2 same legendary minions in standard 

from which 35(29.6%) minions cost 4 or less mana. When you are facing rush any of these minions drawn is welcome (except 2 minions   Lorewalker Cho  and the other is The Darkness)  because before turn 5 there aren't many options that would help you sustain versus a rush such as Paladin, Hunter or Secret Mage besides the minions from the deck and Prince Malchezaar bad boys :) so any of these bad boys comes good before turn 5.

Conclusion so far till turn 5 BIG FAT MAGE versus a rush is welcoming any potential legendary that is under 4 mana which will help you extend the game by trading minions with your opponent, extend you enough to draw a good board clear.

We reached turn 5 safely with let's assume 1 or 2 opponents minion on board cause he is a rush!!! (dam you rushes) so did we manage to pull Dragon's Fury(40% is the chance to have already pulled it into hand around 50% in reality because we have good draw mechanics Coldlight Oracle,  Arcanologist , Raven Familiar )we did that we are doing fine if not we have Prince Malchezaar with 15 possible legendaries that cost 5 mana and could be right there to draw and play inlcuding Prince Malchezaar himself. Although if you not include Prince Malchezaar in the deck the chances are higher to draw Dragon's Fury but the minions that represent 29.6% of all legendaries which are lower than 5 mana adds up to the statistics so basically the difference between  Big Spell Mage not running Prince Malchezaar and Big Fat Mage are slim (talking at point of view against aggro decks). 

PROS vs an agressive decks

Prince Malchezaar has a good chance to grant you good  sustainable legendary minions to put right into play and help you survive long enough to draw good board clears

CONS 

Worst thing that could happen although it is very very rare at turn 5 instead of drawing a Dragon's Fury you draw a Malchezaar's minion. 

The Curator works well with Malchezaar's battlecry because there is 18% each of the legendary cards to be drawn by curator  (1 legendary should be guaranteed to be dragon, murloc or beast each game made by Malchezaar) 

Undoubtedly Big Fat Mage works good versus control all i wanted to clear is that versus an aggressive decks there is not much difference between Big Spell Mage and Big Fat Mage if the Murloc Paladin or Secret Hunter or Secret Mage  have a good start and not so well on your own there is nothing that can stop them only threw right plays you could decrease their chances of winning.