Kobolds and Catacombs Guide
I like the potrait
The best counter class against Gothik the Harvester is Druid, with a focus upon granting the opponent card draw's that result in him running dry, in addition with Poison Seeds to get rid of: Spectral Trainee+Spectral Warrior+Spectral Rider which are summoned upon the death of most of his minion's. Another great way to deal with them would be Wailing Soul but you first get that card from Thaddius which you will first meet in Construct Quarter (wing 4), but it would still leave them useless on the field unless you can buff them.
note: remember Alexstrasza is a must for any heroic boss encounter, but on normal you can deal with him without it. ☺
cant use alexstraza in heroic