How build a special world setting based on "being able to physically enter someone's dreams“?

[Anonym]

In short, I want to build a special world setting based on the following key elements.

people(especially the spellcaster) can enter other's dream physically,just as they enter another plane.
and when they enter someone's dream, everything they encounter are real, and enemies in the dream can literally and physically attack and kill them, and they can also bring objects from the dream———— such as treasure or other valuable resources———— into reality.
for example, when they enter someone's dream and bring a huge box of gold coins and precious gems back to reality, these treasure will be real, and they can repeat this operation in this way to get anything they want and completely unlimited resource supply.
of course, fictional monsters that could only exist in dreams can also come out of dreams and become real creatures forever,and still retaining any strange abilities that couldn't have existed in the real world.

A very important event is:
A poor boy, somehow, allowed an strange ancient artefact enter his dream, which gave him and his descendants miraculous power about dreams.with such power,he went from a poor boy become a king, and the ancestor of all kings of a furture mighty kingdom,and the origin of the entire world setting (the story takes place several dozen centuries later). ——————but he does not know the truth about the ancient artefact.

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So I need some ideas, especially from existing settings. what world setting have such elements aboutf "physically entering dreams and bringing things into reality, or bringing things of reality into dreams"?

 

[ruemere]

Rules. Specifically, to maintain balance between this and dream realities, a law of conservation should apply. Or several of them: of energy, of mass, of complexity (otherwise one could bring in nukes), of space, that is of size and distance (no ant man wannabees, no teleportation), of ecosystem compatibility (no bringing Cthulhu, Freddie Kruger, no xenomorphs nor HIV or Zombie flu) and probably a few others.

Vurt makes for a great book and game of what happens when realities start to overlap.

 

[Tonguez]

Dreamhounds of Paris is a weird Trails of Cthulhu setting where you play historic surrealist artist (like Salvador Dali) exploring the Dreamlands in the 1920s (and going insane)

White Wolfs Changeling the Dreaming, has strong dream themes

Vurt RPG is a cyberpunk dream world

I'm envisioning a Playbook based system where PCs make choices between their Dream (Motivation) or Nigtmare (Fear) as they make soft moves and the Dreaming resist with Hard moves,

Every PC also chooses 1 - 2 Dream Motifs (bridges, roses) and a nightmare Motif which they can deploy to change a dream scene or overcome a challenge 1 -3 Dreamer Points per scene

 

[Richards]

Don't beholders dream themselves into existence nowadays (in 5E, I mean)? Could that be a player in your campaign world somehow?

Johnathan

 

[aco175]

Who determines what the dream is? What would the difference between the real world and the dream world be be then, if there are no different rules between them?

 

[Anonym]

I want to design a key scene,thebeginning of the entire world setting:THE BLOODBORNED PACT


Simply put, a poor boy signed a pact with a mysterious ancient artefact(It actually a living being, but that boy doesn't know this. ), make it to enter his dream from the real world then get incredible power.“Let me exist in your and your descendants' dreams, my power will benefit you and your descendants forever, and in exchange, you and your descendants should be my vessel and then……"

This scene is a very important prelude, implying the entire worldview and their begining, and I havent idea what it would be like(how did a object that existed in real world enter a boy's dream?).
I want some ideas to make it look very dreamy and lovecraftian.