The Boss BF-2 is a flanger pedal used by Prince from the 1999 era to 2016. It appeared on every version of his pedalboard and can be heard on many of his studio recordings. It can be heard on the guitar parts of Paisley Park and She's Always In My Hair, the bass part of 17 Days and the snare drum on If I Was Your Girlfriend.
[On So Far, So Pleased] I ran my guitar through a Boss Vibrato and Flanger. The octave and delay effects are from the Zoom 9030.