Magus Of Possibilities

True to my existence

Between known and unknown

Chasing myriad possibilities

Neither reality nor an illusion

My whole life will be an Eternal Twilight

As for its whole name will be

Eternal Twilight: Recording One's Existence much like Unlimited Blade Works : Infinite Creation of Swords

Describing what it does and a self realization perfectly mirroring the origin and element which will be shown in your magecraft

Once the incantations have been completed, an illusionary Yin-Yang symbol that continuously rotates spreads out to form a boundary and wall for the Bounded Field.

The bright light fills the vision of those present, and manifests an with a scenary divided by a day and night in the distance.

It is a library of knowledge littered with thousands, perhaps a countless number of books scattered in the floor like it was worth nothing, yet are well preserved.

It is a world likened to a library, filled with knowledge, and emotions.

The basis for the world in the Reality Marble is an enternal library that spreads infinitely within his mind. 

note that day and night will be seen on sky having both the Sun and Moon symbolizing between life and death, start and end

The Reality Marble's purpose is a library that accumulates the countless knowledge that are in the form of books, extending into the horizon.

It contains all of the information and procedures for the knowledge for it to be utilized, and it records and analyzes all person and techniques encountered by the user such as magecraft, magus and the likes are all perfectly recorded, allowing for instant proficiency with the knowledge by inheriting all combat skills and techniques utilized by their original owners supplementing the ends limitations

The analysis of knowledge is limited only to the direct use of human senses such as seeing it happen, reading a book, hearing it and so on and so forth.

Shared memories, such as dreams shared with a Servant, can allow for knowledge to be analyzed, even if said knowledge is lost with time such as Primordial Runes , Age of Gods Magic

Note it is not omnipotent because even if you know something it doesn't necessarily mean you know it's weakness or have the requirements to use it well or something specific to someone else such as unlimited blade works

Without being deployed, the Reality Marble allows for storing of knowledge of all his knowledge from what he know and observed

The Reality Marble is a natural counter to most opponents, allowing  him to counter their techniques but it can't bridge the gap between their natural capacity

Once within the confines of the Reality Marble, all of his knowledge are already there not needing to specifically find the one needed

while not in combat it acts as a giant library filled with knowledge while not as much as the root it still has its merit such as combining the existing knowledge so it is a perfect research tool

It's only true limitations are if it is theoretically possible and not specific to a certain race such as divinity