Blue Flute
A Blue Flute is an item that doubles EXP/EHP increment of your Pokémon & Eggs for 30 days.
How to obtain them
They can be found and bought at the Item Shop for 270 Nuggets 
, or for 360 Nuggets where it's included in a Combo Pack with a Black Flute.
They are also sometimes bundled with limited Premium sale offers.
How to use it
It can be blown and activated from your party page.
Other
- Blue Flutes are not tradeable.