Planes of Dimensions.

Here, let me explain this to you :

(I'll use Undertale as a reference)

3D - a regular timeline with regular timeflow. Examples: a single comic/fanfiction/story/etc.

This is what the vast majority of people are within. There’s not much to explain.

4D - the past, present and future of your timeline. Examples: a reset, a SAVE load

If you were to “change” past on this level of existence, the verse would sort you into the probability version your actions have caused. From your point of view you changed the timeline.

5D - the past, present and future of your timeline and all of its possible probabilities. Examples: a timeline, an AU

A single AU is a cluster of infinite probabilities, all connected by a certain constant (for example “monsters are in space”).

6D - the past, present and future of your timeline and all of its infinite probabilities, as well as infinite parallel alternative versions of your timeline. Examples: AUs, the void

Aka dimensional travelers! To hop between AUs you need to traverse the sixth dimension. This doesn’t necessarily mean your “perception” is also 6D - if you’re not simultaneously aware of the existence of all AUs you cannot truly be a 6D entity.

7D - the past, present and future of all timelines in existence and their infinite parallel alternative versions, including all infinite probabilities. Examples: the entire Undertale-verse

We’re finally getting to a single, timeless “everything” limited only by the verse itself. You could say that the entire canon and the entire fandom co-joined belong to this cathegory.

8D - the past, present and future of all timelines in existence and their parallel alternative versions, including all infinite probabilities as well as other alternative multiverses and their own infinities. Examples: verses other than Undertale-verse (for example SU-verse, GF-verse)

You can never be an 8D if you belong, or used to belong, to a specific universe. Because if you do then every universe you visit automatically overlaps with your own universe and creates a crossover. What can be 8D? For example a character that is specifically created to travel across various fiction verses.

9D - the past, present and future of all timelines in existence and their parallel alternative versions, including all infinite probabilities as well as other alternative multiverses, including the ones that are impossible to exist. Examples: the entire fiction-verse

If you were a 9D it would mean you can go into every single fictional story in existence, even the ones what were never thought of (and will NEVER be thought of) in first place.

10D - a dimension that exists above the entire omniverse. Examples: this universe

In other words you, me and everything that is reality. It’s 100% impossible for a fictional character to become real and it’s 100% impossible for someone real to become fictional. And although you can easily create an illusion of interaction between someone fictional and someone real, everything is merely scripted and not a “real” form of communication. Despite us creating fiction and having full control over it it’s not possible to proof that fiction is not a real “alternative reality” we’re actively shaping

There is always a higher level of deimension, kinda like the Matrix.