Soul Stones (a gift from Kuhra)

Ren preforms a ritual to capture a soul of a creature into a rock. The rock must contain life (moss) to be suitable to carry a soul. 

A level is assigned to each rock which determines the level of complexity of the soul that it can carry.

Creatures summoned from the stones do not need sustainance to live. If they "die", their soul will return back to the stone, being able to be summoned after a long rest. They also do not create new long lasting memories.

Note:

If Ren is dead more than 24 hours, all souls in the stones are released and cannot be returned.

If the soul makes a strong connection with Ren and trusts her, then it can have a second chance at life again and be released back into the physical world in mortal form.

A soul can reject Ren's offer to extend their life after death.

If Ren chooses, the soul summons can come out of the stone on their own without being summoned.