Best Deck to Beat Thaddius in Heroic Mode in Naxxramas Construct Quarter
Thaddius in heroic mode strongly relies on minions to win as he summons very strong minions early. His heroic hero ability swaps the attack and health of all minions making it more difficult to beat him with your own minions. The recommended deck to beat Thaddius in heroic mode is Freeze Mage since it you won’t need to summon minions. The deck list to beat Thaddius in heroic mode is shown below.
2x Ice Lance
2x Acolyte of Pain
2x Arcane Intellect
2x Frost Nova
2x Ice Barrier
2x Ice Block
2x Earthen Ring Farseer
2x Cone of Cold
2x Azure Drake
Best Strategy to Beat Thaddius in Heroic Mode in Naxxramas Construct Quarter
Play Freeze Mage as you would normally against Thaddius in heroic mode playing the delaying tactics, like Frost Nova and Blizzard, until you get to turn 9 to Alextraza him. In turn 10 play the burn cards, like Pyroblast, Fireball and Frost Nova, to kill Thaddius.
Note that it might take a few tries and a good starting hand to beat Thaddius in heroic mode.