Also juuuuuust a theory...
----- don't look into it too much-----
So...the parents mentioned that the other is a being that can form into ANYTHING as long as it's in the mind of the host. It's just a theory but when the parents said "the other" is already inside all of us (don't make this into a lewd joke pls.) Does that mean its somehow connected to echo? I mean smoke room gave hints of adastra in it so why not? And furthering this theory, The parents mentioned that "the other" takes the shape in which what you think, this includes fears, so maybe thats what the spider, deformality, and monster that was shown to chase but not noticed by his friend's, But, what if the other really did have a physical form? I dunno, Maybe THE CREATURE THE ATTACKED OUR GOD D*MN VAN !?
[this part of the post has been redacted due to graphic visualization]
But again, this is just a theory so don't look into it too much ^^
-ace ayasaki