Low-Budget Chromaggus Mage Deck (Heroic Mode)

Strategy

Although this deck is a strong choice for defeating Chromaggus, it does rely on a strong start. You will need to mulligan aggressively for Mad Scientist and Sorcerer's Apprentice in order to gain an advantage in the early turns. Mad Scientist will Deathrattle into a Secret, that will either allow you to copy a powerful minion, usually a 4-drop, or will block one of his expensive spells like Swipe or Bite. Sorcerer's Apprentice is used to discount the cost of the Brood Affliction cards in your hand, and allow you to start discarding them earlier than you normally can in other decks.

Once you have been able to achieve this strong start, the fight becomes more straightforward. The key to defeating the boss is correctly managing the Brood Affliction cards that you are given at the start of each turn, and identifying which ones you should prioritise discarding first. As a general rule, the card that does damage to you, and the card that heals Chromaggus are unimportant, and can be ignored for several turns. The cards that modify the costs of Chromaggus' minions and spells, however, are far more important, and should be discarded immediately.

The deck plays several tech cards to make your life easier. Firstly, the 2 Big Game Hunters are fantastic for dealing with many of Chromaggus's late-game threats like Alexstrasza and Nozdormu. Emperor Thaurissan can be used to discount the Brood Affliction cards in your hand even further, while Mountain Giant can take advantage of your hand being filled each turn.

Once the game reaches the point where you are able to get Kel'Thuzad into play, your victory is almost assured, since the enemy AI plays very poorly against this card. You can simply use your minions to trade with his on each turn, and develop an overwhelming board which he will never remove.