It starts with a new experimental drug created by Luna called Dreamscape.
A magical dust that when inhaled, will put you in a near immediate lucid dream where you have full control over your dream as you sleep.
This is to aid Luna during her long nights defending Ponies from their nightmares at night by giving them this power.

A young buck, obviously with a vore fetish, uses this drug in a commercial to dream up his perfect waifu pony, or better yet, Sphinx to fulfill all his desires, especially the vorey ones.

As he uses it night after night, his dream wife, she starts gaining new abilities, like the ability to alter her size as he wished, though able to completely devour him even when she's a bit smaller by making her body completely flexible.
She also started talking to him and to his surprise, remembering previous dreams he had with her.
One morning after he slept without the drugs effect, he awakes to find his dream wife with him in his bed.

It turns out that the Dreamscape drug had one or two little quirks about it.
One being that in order for you to have control during the dream, the dream is given a light sense of awareness and sentience that quickly fades after a couple days.
The other is the warning that this drug is supposed to be taken only once a week.

Now a part of the Physical realm, Amet has a vast amount of abilities available to her, such as shape shifting, control of her size and insides, capable of walking through walls and such.

She would need a supply of Dreamscape to keep herself in top form in the Physical realm, though she can re-enter the Dream realm by going into a sleeping figure, she can also enter their dreams specifically if she wished.

She enjoys having fun with others, be it normally or more sensual and in either realm, hopefully you'll enjoy having fun with her too.