Boss OC-2 Octave
An octave pedal used by Prince from 1982 to 2016. It appears on every version of his pedalboard and can be heard on many of his studio recordings. It can be heard on the guitar part to Darling Nikki and the drum parts of Hot Thing and Forever In My Life. The effect on the bass solo of Crystal Ball comes from a glitching OC-2.
It was also used by Sonny T.