Soul Harvest
Client records describe this reading. They do not confirm availability in gameplay.
Current client record
Killing a non-trivial target afflicted by your Drain Soul increases your Mana regeneration by 100% for 10 sec and allows 100% of normal Mana regeneration to continue while casting.
Sourced change history
No changes in the tracked log could be matched to this record. This does not mean the ability or item has never changed.