For this Trophy, you must talk to all of Sonic's friends. Friends can be found in the hub world at the entrance of a level, frozen in time until both acts of a zone are restored by playing as both Classic Sonic and Modern Sonic, with the exception of the very first zone, which unfreezes a character for completing Act 1 and another for completing Act 2. The rival characters such as Metal Sonic, Shadow the Hedgehog and Silver the Hedgehog don't count, despite the latter two being Sonic's friends, though you'll talk to them regardless since you must accept their challenge so you can take their Chaos Emeralds which are required to fight the final boss. The characters that need to be talked to are.
Classic Tails
Location: Green Hill entrance
Notes: Will only appear when playing as Classic Sonic.
Modern Tails
Location: Green Hill entrance
Notes: Will only appear when playing as Modern Sonic.
Amy
Location: Chemical Plant entrance
Knuckles the Echidna
Location: Sky Sanctuary entrance
Cream the Rabbit
Location: Speed Highway entrance
Rouge the Bat
Location: City Escape entrance
Espio the Chameleon
Location: Seaside Hill entrance
Blaze the Cat
Location: Crisis City entrance
Vector the Crocodile
Location: Rooftop Run entrance
Charmy Bee
Location: Planet Wisp entrance