An Astral Splinter is an entity whose conception happened to occur at the very same moment a "piece" of the Astral Plane superimposed itself unto the Prime Material Plane. The resulting effect creates an Astral Splinter an entity whose soul has accidentally stolen a "piece" of the Astral Plane. With their material body being suffused in the astral they do not project themselves into the plane as much as step into it., allowing them to slip between the two planes as easily as walking through an open door.

Since an Astral Splinter is a "piece" of the Astral Plane itself they have access to an unusual array of magical abilities. While an Astral Splinter does still have access to the more classical magical means, they are harder to use and less inclined to agree with the Astral Splinter. (All none Psychic and Force magic consumes 2 Spell Slots to cast for its level if it is not cast as a Ritual.) What an Astral Splinter lacks in classical magical means, they gain in unique abilities only available to them. An Astral Splinter can access the Astral Plane at will, strike at the astral self of others,  create an astral domain within the Astral Plane, store magical energy within an astral domain, and travel between other Planes via the Astral Plane.

Awakening

The awakening of your deep-seated astral connection has occurred, flooding your very being with a tsunami of untapped potential. At the 1st level, you unlock the Mind Sense, Astral Shift, and Empathy spells. These three spells are your cornerstone to a very promising future. 

While operating the Astral Plane opens you to Psychic abilities it also, opens you to Psychic abilities. You are more vulnerable to attacks from Psychic magic and Psionic ability users.

Resonance

At the 6th level, the "piece" of the Astral Plane within you resonates with your growing power and control.  Within the Astral Plane, you are now able to exert more control and dominance. Stake your claim upon the Astral with the Circle of Self ritual spell and exert your presence upon others with the Astral Hand spell.

Dreams and Reality

At the 14th level, your connection to the Astral has undergone a transformation like a thin branch over a creek that has become a grand bridge over a canyon river. You gain access to the spells Imagination and Pocket allowing you to further blur the line between dreams and reality. 

Your influence over the Astral has tempered your mind, body, and soul, increasing your resistance to Psychic and Force attacks.

Astral Monarch

At the 18th level, your place in the Astral Plane has become solidified. Having transcended your abilities you gained the ability to project into the Material Plane from the Astral Plane through the Avatar of Self spell and the power to juxtapose your Astral Domain over Material Plane through the Palace spell.

Having stamped your existence into the timeless existence of the Astral Plane, you gain immunity to Psychic damage.