Marvin, who was speeding away at the other end of the Nightmare Boundary, naturally wasn't aware of the discussion between the two powerful existences of the Universe.
After obtaining the Crystal Statue, he had to find a way to leave this world, which was an external plane.
Although Marvin could enter the Shadow Plane, he only had the coordinates and the ability to freely pass into the Shadow Plane from Feinan.
If he tried to rush into the Shadow Plane from here, he might enter a strange area be swallowed by Shadow Monsters hiding in the Shadow Plane.
Just as Louise said, coming to this plane was very dangerous.
At that time, Marvin was confident that he could leave, but Louise jinxed it.
He couldn't leave the Nightmare Boundary.
As soon as he escaped from the ancient well, Marvin used the tool made by Madeline to create a temporary Teleportation Gate that would lead to White River Valley.