The PURPLL is a phase-locked loop (PLL) type pedal. It can be used as a fuzzed out harmonizer, drone synth and more. Check out the videos and the manual linked here for more details.
Blem units are new pedals with some sort of cosmetic defect. Such defects may include: small scratches on the surface/paint, minor engraving issues, and/or significantly outdated backplates. The defects are typically minor but you can see some images of pedals that were sold as blems in the gallery linked here. Such units have the same warranty as standard/mint units, however they cannot be returned for cosmetic reasons.