How does the mana regeneration portion of Improved Drain Soul work?
YOU have to get the killing blow in order for it to proc. If anybody in your group/raid gets the kill, no Improved Drain Soul proc for you. You have to finish the mob while channeling Drain Soul, meaning that you’re probably going to be relying either on a nuke that flying towards the mob or DoT’s to benefit from Improved Drain Soul. In the case of the nuke, it will be nearly impossible to get the shard if the mob is in your face.