Niko's shop is a shop in which you can make or buy extracts which requires Mushrooms to be made.
It is found on Treebranch Town, but can only be accessed after Mushroom Maniac Quest is finished.
For a shortcut, after visiting the shop, go to Town People under town, and click Niko's Shop
Every day you can buy a mushroom for 5,000 Omega In-Game Currency
and you can buy a perfect extract for 50,000 Omega in-Game Currency.
Guide to Mushrooms:
Mushrooms are used to make Extract.