Powerberry Location
There are 9 Powerberries and one special blue Powerberry. Here are their locations.
Hoeing your fields. This Powerberry will appear randomly.
Go to the Goddess pond with full strength. Throw in a crop from your farm and wish for strength. The Goddess will give you a Powerberry!
Go to the Fisherman's pond during winter if you have a golden hammer. Smash the giant rock with a full charged swing to get a Powerberry.
Buy a Powerberry from Sammy the Salesman at the Festival. It costs 1000G.
In the mine, dig around until you get to the third or fourth floor. Hoe around until you get a Powerberry. It's tough to get this one. This Powerberry will appear randomly.
Win the egg festival for the first time to get a Powerberry.
Go fishing off the pier at the beach during Spring. Eventually you'll catch a Powerberry. This Powerberry will appear randomly.
Plant a lot of pink cat-mint flowers. Stu will come by one day and ask if he can trade you a marble for some flowers. Say yes, and then bring the marble to the harvest sprites. If you're their friends they will give you a Powerberry for the marble.
Last (9th) Powerberry
Befriend Lillia and Basil. The next year Basil will give you a Powerberry.
Catch a fish and toss it into the middle of the fisherman's pond. Note it must be the dead middle or it will not work. If done correctly, an imp will come out and give you a blue Powerberry. This enables you to work in the rain without getting sick.