Supernatural (2005)

S11E8 Just My Imagination

Sam is taken aback when his long-lost imaginary friend, Sully, suddenly reappears in his life. Confused about this unexpected visit, Sam is even more astonished to discover that Dean can also see Sully. Through a series of flashbacks, the episode explores young Sam's bond with Sully and the reasons behind his need for such a companion during his childhood.