Resurrection

The one that made it the furthest in the underground, perseverance. Perseverance had beaten almost all of the monsters in the underground from papyrus to sans and undyne but ultimately couldn't finish the task of beating asgore and so his soul was took from him. However, years went by and his soul was left in the underground along with the other six after Frisk had broke the barrier but this changed when gaster had finally been freed from his hell