There are no item maniacs or collectors in Pokémon X and Y so you can only sell items at PokéMarts.
there isn't one you just sell the mushrooms
Any store most likely.
They can be given to the Move Relearner to teach a Pokemon a Move it's already learned in FireRed and LeafGreen, but serves no purpose other than to be sold in Diamond and Pearl.
Nuggets are just used to sell. Each one is worth 5,000 dollars. Tiny and Big Mushrooms are items to sell at pokemarts and are worth 250 for the tiny mushroom and 2,500 for the big mushroom
There isn't one. You just sell the mushrooms.
Nothing unless you would want to sell the for some money
A mere Cameo appearance from Firered and Leafgreen. They do no good, so you may as well sell them.
You take them to the food maniac, in her camper van, on route 5.
After beating the elite four, talk to Bill's friend in One Island. He'll give you a mission that gives you the ability to trade from Pokemon Emerald, Ruby, and Sapphire. Bill's friend will give you the rainbow pass which will give you the ability to encounter islands 4-7. On island 4, talk to the guy in the house next to the Pokemon Center. He will teach your Pokemon a new move if you trade him the Mushrooms. This works in FireRed and LeafGreen.
Around £10.00 I'm A Collector Myself!
You sell them
On Ebay.