Any point on the line can be described by a single coordinate, so the line is one-dimensional.
We could also describe all of them in terms of a two-dimensional plane [(0,0), (0,1), (0,2) etc.] but that would just be redundant. Just like representing the number line with a taller figure doesn't really make the abstract line any different:
So for a single-pixel wide view of SMB from first person perspective, we could consider it a degenerate case of a 2D view if we indexed them (0,1), (0,2), (0,3)... but that would be redundant as they're sensibly just 0, 1, 2...
Consider that any 2D image you see on your screen is just a single-pixel deep 3D image and a single-pixel 4D-protruding 4D image and so on.
Now I think the original question was about how Mario is capable of seeing at all something that is 1D, in the sense of "how are Mario's physical eyes able to perceive something that has only 1 dimension".
And he's right, Mario wouldn't be able to see a mathematical line (i.e. something truly 1D and infinitely thin), because there'd be nothing to reflect light for his eyes to perceive. I think the answer here is that Mario isn't an animal with animal eyes, and his fictional "vision" must work in different ways so that he can perceive purely 1D "mathematical" lines.
We could also describe all of them in terms of a two-dimensional plane [(0,0), (0,1), (0,2) etc.] but that would just be redundant. Just like representing the number line with a taller figure doesn't really make the abstract line any different:
So for a single-pixel wide view of SMB from first person perspective, we could consider it a degenerate case of a 2D view if we indexed them (0,1), (0,2), (0,3)... but that would be redundant as they're sensibly just 0, 1, 2...Consider that any 2D image you see on your screen is just a single-pixel deep 3D image and a single-pixel 4D-protruding 4D image and so on.