Moon Flute

From Pixelmon Generations

A Moon Flute is one of two types of flutes that can be used to summon a wormhole to enter the Ultra Dimension. When the time is night and a Celestial Altar is blue, the altar can be clicked on with the flute to summon a wormhole. For a wormhole to successfully spawn with a Moon Flute, a Lunala or Necrozma is required to power the altar. The Moon Flute can not be crafted, but can be dropped from legendary and Ultimate Boss Pokémon.