The fifth Green Goblin was a genetic construct, created with the sole purpose to serve as Norman Osborn's flunkie and help clear his name. Norman had recently returned from Europe and needed to divert all public suspicion from ever associating him having been the first Green Goblin.
Norman would order the fifth Green Goblin to attack while Norman himself was in the vicinity of these attacks, such as having him kidnap his grandson Normie.
Norman later ordered him to break Roderick Kingsley out of jail when Kingsley falsely claimed to have a journal with proof that Osborn was really the original Green Goblin. During the midst of a battle between Orborn and Kingsley, the fifth Green Goblin battled Spider-Man, who managed to pull his mask off. However, the flames and smoke that resulted from the intense battle obscured his identity.
Later, the fifth Green Goblin returned, and in the midst of a battle with Spider-Man, he began to disolve thanks to the Goblin Formula coursing through his veins. When unmasked, his face was able to morph and change to a variety of faces, primarily that of Harry Osborn. He eventually warned, just before fully disolving and breaking down, that "he" would return. It is most likely he meant Norman Osborn, who was lying low at the time.