Then play as Shale and just cast Heal as often as possible - make sure as Shale you stand by the button. If you haven't, set all of your team to use a small heath potion at 75% health, and a large health potion at 25%.
I had to get rid of about four or five whilst we hammered away at him. When the Harvester is very close to the end of his first form, wait until the last possible second to push the button, this way you can clear most of the skeletons he summons. Defeating the Harvester on Hard or Nightmare difficulty is nearly impossible if you just try to tackle it without strategy.
