Amazing Spider-Man #800, written by Dan Slott and featuring the work of six iconic Spider-Man artists, not only featured Spider-Man’s climactic battle with the Red Goblin but acted as the finale to Slott’s decade-long run on the title. As you’d expect, it came with lots of surprises, including a new twist on an old favorite Spidey costume.
Warning: full spoilers for Amazing Spider-Man #800 ahead!
Given that Red Goblin was a fusion of Green Goblin and the Carnage symbiote that combined all of their strengths while eliminating their weaknesses (namely sonics and fire), Spider-Man needed his own edge to take down the villain. Eddie Brock took a beating fighting the Red Goblin as Venom and was down for the count, so he gave his symbiote to Spider-Man in order to help level the playing field. The result is Spider-Man once again wearing the black symbiote costume:
Source: IGN.com Amazing Spider-Man Finale Features New Costume