Ty @Artyeevee for this suggestion, Wisp matches well to be Toriel, and if she's casted as Toriel, that makes Shard casted as Asgore!
Wisp will be your guardian on either route, but depending on if you chose Genocide Tala or Pacifist Emerald, that will choose Wisp's fate in the end. When you battle her, she won't use fire, but aura that helps her phase to a ghost and back.

#Mobitale