Communing is the power to speak with and return spirits that have no crossed over the mortal plane to resolve unfinished business. However, not all spirits come back, as only a few were mentioned to come back.
The user appears to have little control over which spirits he brings across and does not know what their unfinished business may be. It also seems that the user can only bring back spirits that died in the current location they are using the power in, or spirits that are related to people close by him.
Unlike typical ghosts, the spirits returned are fully-physical beings that are capable of touching, eating, becoming drunk, using drugs, having sex and even killing.