The day Monster kind was sealed into Mt. Ebott, the mages added a little extra insurance. A curse.
Human SOULS may pass. But Human forms may not.
Young Frisk must navigate the dangers under the mountain, a little less human than before...
Don't stop now, I want to see all this pain and suffering lead to a happy ending where all the lost come back and the humans are still Monsters. What can I say the design on the brothers is worth it alone and oh God your Undyne is pure goddess. And then there is Metatton, Hes like a dark David Bowie and I love it.
But I really wanna see fish girl and her happier times.