A few years ago I read a book where a kid (I believe in first person) was part of a group of chosen kids. The main character entered a room (in an alleyway?) where he was supposed to choose an object special to him. The main character saw a floating Earth that mimicked reality (water felt cool, the grass fresh smell, air breeze, n/s poles). He ended up choosing a special box of some sort. The other kids already chose their objects.
Another kid was a girl who had a necklace to go through objects. These monsters who can copy abilities copied the girls abilities and chased her in the ground when she turned off her powers and killed one of the, inciting rage for the others. There were 3 of these I believe. They were a threat throughout the whole story.
Hardback Book in English, I don't remember the specific year I read it
