Downed Necro Worked
He went down against the Throbbing King. He had the leech one, the heal, and Haunt w/ +6 Corpse health. Though it appeared that the healing from the leeches also healed the corpse.
The infinite range helped deal constant damage in Phase 2 and the healing was upgraded so that helped too. You definitely need to make sure you have some key pieces in place, but it's surprisingly powerful.