Bipper is Dipper Pines from the show Gravity Falls, possessed by the psychotic dream demon, Bill Cipher.
Dipper’s mind is separated from his body, trapped in The Mindscape. Bill causes self harm to Dipper, exploring his new body, and sees pain as a joke. 
Bipper is maniacal and known to be somewhat of a masochist. He thinks pain is "hilarious”. He severely overestimates - or is not aware of - the physical limits of the human body.
Dipper's consciousness is forever haunting Bipper.