This is found in Autumnal Avenue, beside a taxi cab on the way to the Prism Tower. You can buy pre-mixed juices from the man on the left side of the counter but you can only choose once per day. The lady to the right can mix various berries to make them as a juice/shake. You can't keep the purchased or mixed concoction so you'll have to give it to one Pokemon in your party.
One thing you can not is that the price of the juice seems to determine the value of the stat that will be boosted. A P400 juice will increase 4 points while a P600 juice will increase the value by 6.
Note: For juices that increase the EV values of a pokemon, they'll increase happiness instead if the Pokemon has maxed out the specific EV the juice was supposed to increase.
Ultra Rare Juice | Increase Pokemon's level by 5 | Sold in the left counter |
Rare Soda | Increases Pokemon's level between 1-4 | Mix Lansat Berry + Starf Berry |
Colorful Shake | Increases happiness | Mix berries with different colors |
Purple Juice | Increase HP by 4 to 32 | Mix two purple berries |
Red Juice | Increase Atk by 4 to 32 | Mix two red berries |
Yellow Juice | Increase Def by 4 to 32 | Mix two yellow berries |
Blue Juice | Increase Sp. Atk by 4 to 32 | Mix two blue berries |
Green Juice | Increase Sp. Def by 4 to 32 | Mix two green berries |
Pink Juice | Increase Speed by 4 to 32 | Mix two pink berries |
Perilous Soup | Removes all Effort Values on a Pokemon | Mix Kee Berry & Maranga Berry |
Source: Serebii.net