There are also several unused lines, fully voiced by the game's English cast. Notably, some of these lines hint at scenes removed from the game's Last Story, 2 of which featured the President and his secretary, the latter (as well as Amy) telling the President not to give up hope and a scene that would take place shortly after Finalhazard's defeat, where the President says that, as a child, he admired heroes like Sonic and aspired to be as heroic and beloved as him, with the Secretary offering encouragement.

Another set of lines that would have appeared during the ending credits feature Eggman declaring he'll conquer the world without anyone's help, as well as him and Tails agreeing not to hold back next time they meet.

During the scene where Team Dark meets with Amy, Eggman says the line, "Aaah, Amy you're timing is impeccable!" which is grammatically incorrect. The line should have read, "Aaah, Amy, your timing is impeccable!"

Like Sonic Adventure, Sonic Adventure 2 has hidden wallpapers that can be found by inserting the Dreamcast disc into a computer's CD drive.

There is a variety of unused data in the games code. Some of which was featured in later remakes. The unused content includes art assets, text that suggests a World Ranking system was in the works, extra tutorials, and added Chao World features. Unused content present in later versions include the Black Market and unused themes (Shadow, Amy, Omochao, Maria and the Secretary).

A number of Omochao lines were removed from Sonic Adventure 2 but were re-added as an Easter egg in Sonic Adventure 2: Battle for when Sonic or Shadow carries Omochao through the goal ring.

Big makes several cameo appearances in Sonic Adventure 2. He can be found in most stages and boss fights, and even some cut-scenes if you look hard enough.

According to an unused audio file for Omochao, Eggman's mustache is fake.

In the Dreamcast version of the game, boxes in the Crazy Gadget area have green X's on them. These were changed to red X's for the Gamecube version of the game. It's believed that the change was made because the logo of Microsoft's Xbox is a green X.

Sonic Adventure 2 was sponsored by the shoe company Soap, which is why Sonic's shoes are different in this game. In addition, Soap's gimmick is that you can grind rails with them, a move that was added to Sonic's arsenal. Even after the deal expired, grinding became a series staple.