I can't make sense of this spell. It seems to be missing the actual effect part of the spell's description.
You plunge the targets' minds into a veiled immersive mindscape of your own design.
Okay, that's flavor text. What is a "veiled immersive mindscape"? What does it do to the target?
The next two sentences detail how creatures with different numbers of hit dice are affected, and what happens to the duration if they succeed on their saves.
Given time, the bodies of creatures whose minds are trapped in a microcosm can die of starvation and thirst without care.
So I guess they're trapped in some fashion? Are they conscious? Are they aware of their surroundings? Does their body fall prone? Can they communicate in any way? Can they take actions of any kind? Could a creature inside the trap cast Wish to escape?
That is not flavor text. That is a game term. The rules for mindscapes are in Occult Adventures.
Veiled: The veiled immersive mindscape is the most insidious type. Its triggering mechanisms are designed to fool the target, trapping the creature in such a fashion that it doesn't realize its reality is a product of its or another's mind. The creator's memories provide the basis for the mindscape, and any place or phenomenon she hasn't experienced might be hard to replicate convincingly using only her imagination.
Immersive MindscapesAn immersive mindscape is a less common, but far more powerful, variety of mindscape. When created, it seems every bit as palpable and vivid as the real world. A being within an immersive mindscape can see the land, feel the breeze, hear the falling rain, smell the sea, and even experience hunger and thirst. In some cases, creatures within an immersive mindscape don't even realize that's where they are. A target that's fooled into believing such a mindscape is real wastes away in the physical world while living a full life in the mindscape.
An immersive mindscape can be sculpted in much more detail than a binary mindscape, and its traits vary. The creator dictates the traits of an immersive mindscape, and visitors are subject to whatever strictures the host is able to place upon the mindscape. The construction of the mindscape might be carefully designed, or might be a more instinctive expression drawn from the creator's own desires or intentions (whether conscious or subconscious). Some spells allow the creator to use a target's memories or desires when creating the mindscape to better fool the target.
Mindscapes are temporary constructs of the mind that come into being on the Astral Plane and fade away again, in much the same way a sleeping person's imagined landscape forms and dissolves while he is dreaming. The primary difference between a mindscape and a dream is one of intent; a creature often deliberately and precisely constructs a mindscape, while a dreamer typically does not. A mindscape can come into existence as a result of creatures engaging in a psychic duel, as well as through certain spells, magic items, rituals, and other occult phenomena.
In theory, a mindscape can take on any form or appearance—and can possess any conceivable trait—in much the same way the various planes do. In practice, mindscapes often either appear mostly normal, or feature only one or two traits that stray from reality, and creatures' psychic avatars manifesting within the mindscape might not be able to tell they're no longer in the real world.
Two types of mindscape exist: binary mindscapes and immersive mindscapes. Binary mindscapes occur during psychic duels, when a creature with psychic powers draws another into a mental battle. Only two participants can occupy a binary mindscape. This cerebral combat arena does not totally engulf the participants' senses; a creature engaged in a psychic duel within a binary mindscape can still perceive the real world, but is largely consumed in her psychic battle. In this case, the mindscape is a powerful image in the mind's eye, perceived on an abstract level and capable of affecting the subject in the real world, detaching her from events in the real world but leaving her still capable of perceiving them.
Immersive mindscapes are far more tangible and realistic. In an immersive mindscape, a creature's every sense perceives its imaginary surroundings completely, in effect replacing the body's actual sensory perceptions.
While a creature's consciousness is within a mindscape, that creature's body in the real world can take no actions and loses its Dexterity bonus to AC, but it isn't considered helpless, as the unconscious parts of the creature's mind still provide resistance to the creature's destruction. While in an immersive mindscape, the mind gets no information about what the body sees, hears, smells, or touches. Thus, if the body takes damage from an attack in the real world, the mind remains unaware of it. A binary mindscape, however, allows a creature to monitor its own condition in the real world.