Right after the end credits and the archival clips finish rolling, the words "HAPPY BIRTHDAY SONIC!" appear, as well as a screaming crowd yelling those words. You deserve it after all these years, Sonic.
It's more Heartwarming if you know that that crowd are real Sonic Fans all over the world that Sega asked to record in several events to use in this game.
"Hey, Sonic! Enjoy your future, it's going to be great!"
Silver's reason for fighting Sonic on any repeat plays of his Rival Battle? Just for Fun.
Right at the end, Classic Sonic attempts to repeat his older self's homing attack. Doesn't work right at first, but Modern Sonic applauds and tells him "You're going to get better!"
Maybe it's just this troper, but when the Time Eater attacks, What do both versions of Sonic do? They immediately rush to put themselves between Tails and danger.
It's even better in the 3DS version. The Sonics are down for the count. The Time Eater tries to finish them off, but the Tailses shield them.
Modern Sonic: Tails! Are you okay?!
Modern Tails: Owww. I think so...
Modern Sonic: Why did you do that?!
Modern Tails: Heh heh.
Classic Tails: I wanted to help, too... Sorry, Sonic.
The end credits showing 20 years of Sonic history in gameplay and music can really warm the heart of a lifelong Sonic fan. It shows that even throughout 20 years, all the Sonic games and their nostalgia is appreciated by both the fans and SEGA.
Sonic's friends cheering both Sonics to stop the Time Eater and both versions of Dr. Eggman before the Final Boss fight.