Yeah, as said, gotta be more than 20 Stranger missions. I'm about 4 hrs in, 5 story missions or so and have done 8 stranger missions or so. I think there's like 60.
301 completed games to 100%
90.39% completion percentage
Last Achievement : Sonic Finale - Sonic & Knuckles (Xbox 360) - 25g
Last 100% Completion : Sonic & Knuckles (Xbox 360)
Thanks to Rajeanero for the avatar and Xerofox for the sig.