Urban Elf: If you win the battle, you will drop a treasure chest

Xu Ying traveled to a world where humans and elves coexisted.
There is a secret realm full of dangers here.
There are dangerous and rare elves in the secret realm, as well as various precious props, and a passage to another world!
Countless trainers regard the secret realm as a place to rise, eager to get rich overnight in the secret realm!
But the danger of the secret realm has also cost countless trainers their lives.
However, for Xu Ying, it seems that it doesn't matter whether he goes to the secret realm or not?
"Hint: You defeated a Rattata. Open the bronze treasure chest and you get an ordinary Poké Ball."
"Hint: You defeated a Kentero. Open the silver chest and you get magical candy."
"Hint: You defeated Suicune and opened the diamond treasure chest, and you got..."