Soul Harvest is a Terror Witch Doctor skill unlocked at level 9. This skill has changed a great deal during development, and is now a buff that boosts the Witch Doctor's spell damage when there are numerous enemies in the vicinity.
The Witch Doctor gains strength from the close proximity of his enemies.
Skill Rune Effects
The following is a very quick summary. See the Soul Harvest rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
<skill class="WitchDoctor">Soul Harvest</skill>
This skill was initially a nova-type of attack, one that dealt damage and fed mana back to the Witch Doctor for everything it killed. That changed entirely during development, and the skill now buffs the Witch Doctor's spell damage.
I seldom needed it, and found it to be less than effective as a killing weapon. It wasn’t that damaging, and wasn’t that cheap to cast either; so I had to make sure it was going to kill at least a few monsters to be cost effective.
The old version of this skill created a nova-like ring of blue smoke around the Witch Doctor. All targets within the ring were damaged, and if the damage was enough to kill them, their souls (white/blue ghosts) swirled into the air, then down into the Witch Doctor, where they added to his mana. The skill was just the same at BlizzCon 2009.
Soul Harvest was changed entirely for Blizzcon 2010, becoming a Tier 3 buffing sort of war cry. Unfortunately, there are no gameplay reports detailing any usage of this skill from that event.
Skill tiers were removed shortly before the beta started in September 2011, and Soul Harvest became a level 14 skill. Soul Harvest was one of the skills available in the BlizzCon 2011 PvP Arena, and Adivirgi enjoyed using it:
This is a crazy awesome spell that lets you damage multiple enemies and receive a pretty decent damage buff at the same time. Its downside is that it also has a very short range so you basically need to be right in the middle of a pack to get the maximum effect for this spell.
Unfortunately, putting yourself "right in the middle of a pack" is a very dangerous thing to do in the Arena. This skill is much more useful in the regular game, where running into a pack of enemies generally won't kill you instantly.
The skill system was once again overhauled for the Beta Patch 13 in February 2012, and Soul Harvest was classified as a Defensive skill and moved up to level 22. For Beta Patch 15, it was re-classified as a Terror skill, moved back down to level 9, and had its mana cost increased.