The Harvester appears similar to that of the Summoner. It has a blue and red skin tone and a large yellow rune in the center of its chest. Its skull is shaped similar to a Hell Knight, albeit with a large yellow eye and two large orange horns.
The Harvester has a 'beam attack' that, whilst damaging enemies, allows the Harvester to absorb their life force. However, this beam does have a limited range. The more health/armor an enemy has, the more life force the Harvester will gain. The Harvester's 'detonation attack' is charged by absorbing this life force, and when unleashed, fires several large plasma shots similar to BFG shots, but without the damaging rays.
When fighting against a Harvester, long range attacks are recommended as its beam attack has a limited range.