- Acting in the Dark: The voice actors all recorded their lines separately, their scripts only had their respective characters lines, and absolutely zero story context was written in or given to them, even if they were talking to another character. Not helping was that voice director Lani Minella's direction only amounted to "sound excited" or "sound angry".
- Christmas Rushed: The game was rushed for its original Japanese release and was loaded with glitches, forcing Sonic Team to delay the U.S. release by a year to patch it up. Even then, the game still has loads of glitches, so it's very easy to break wide open, most notably in the DX port, which adds even more glitches than the original Dreamcast game.
- Creator Backlash: Jon St. John, Big the Cat's original voice, has so much regret and hatred for voicing Big that he purposefully forgot how to do the voice.
- Keep Circulating the Tapes: The original Dreamcast including the Christmas and Halloween DLC's, have never been added into any of the ports or remakes.
- Killer App: This was meant to be the showcase game for the Sega Dreamcast, along with Shenmue. Unfortunately a relatively sloppy launch version in Japan tanked some of its release hype. This was patched up for the western release the following year but gaming media outlets had gotten word of the Japanese version, which may have soured some people on the game before they knew the western release was going to be smoothed out. The cleaned up version also ended up being released as Sonic Adventure International in Japan. Nevertheless, the game became the Dreamcast's overall best-selling title.
- Moved to the Next Console: Adventure started out life as a late-in-life Saturn title using the "Sonic World" engine from Sonic Jam.
- Playing Against Type: Jon St. John, most known for playing the sociopathic machoman Duke Nukem, plays the role of the kindhearted simpleton Big the Cat in the English dub.
- Saved from Development Hell: This wasn't the first attempt to bring Sonic to (non-isometric) 3D platforming. Sonic Xtreme for the Sega Saturn was supposed to do this, but turmoil within the company over the game's direction reduced it to Vapor Ware. According to Sonic co-creator Yuji Naka in an interview for the first issue of Official Dreamcast Magazine, SA1 was at one time supposed to be a Saturn game, but the idea was scrapped when the company decided to focus on the Dreamcast. The work done on the Saturn version was repurposed for the 3D "Sonic World" level in Sonic Jam, which is the closest the Saturn got to a 3D Sonic title.
- Urban Legend of Zelda:
- After the release of Sonic Adventure 2, a rumor circulated around the internet that said that Shadow could be found on the other side of the train in Station Square. Said train has an Invisible Wall over it, specifically to prevent people from jumping over it, but that didn't stop people from trying to anyway.
- Similarly, there was a rumor that Fang the Snipernote was a Bonus Boss that could be encountered at Tails' Workshop after completing the game. This probably has something to do with his planned appearance in Sonic Xtreme.
- What Could Have Been:
- As stated above, Sonic Adventure was originally in development for the Sega Saturn, with the Sonic World featured in Sonic Jam serving as a prototype. As such, there are some elements from Jam that can be found in Adventure such as some of Sonic's animations and an unused spring that can be found via hacking.
- According to some Dummied Out voice clips from Tikal, Super Sonic was going to be playable in the same manner as the Genesis games (collecting 50 rings will let you transform during a level). Although its possible that Metal Sonic skin uses the unused code for it.
- The in-game engine appearance of Perfect Chaos was supposed to match how he looked in the game's FMV intro and the mural found in the Lost World level, but graphical limitations prevented this from happening. When the fight was remade for the 20th anniversary game Sonic Generations, he was given the intended design since technology had improved enough to allow for it.
- Speaking of Chaos the final boss was drastically different having Super Sonic travel on top of a barrier and attacking the tentacles to break through the base to defeat Chaos. The idea was simplified in the final to running at great speed in a straight line to attack hem. This idea for a final boss was used in the game Sonic Unleashed.
- It would appear that early on in development, the characters (or at least Sonic) would've retained the designs they had in the Genesis games. If one looks closely during Sky Chase in the Dreamcast version, Sonic's model resembles his classic designnote . The Sonic pinball table in Casinopolis uses the characters' classic designs. Then there's this tutorial image from the Dreamcast version's website◊ and an old storyboard for the intro uses his classic design.
- A very early Dreamcast prototype, called the "AutoDemo", has been unearthed and searched through. 3 test maps and many early maps were found, but the biggest find was the map geometry of the early Windy Hill, as seen in the game's earliest promotional materials and in the intro cutscene. The map, along with structures in the test maps, suggested that the game would have been more dependent on Sonic's momentum, rather than his raw speed, and may have featured physics similar to the Genesis games.
- Most of the characters had different animations reflective of their unused abilities.
- Knuckles at one point had more combat heavy abilities such as uppercuts and takedown punches which were seen in the earlier promotional videos of the game. Animations for them can be found in the demo.
- An unused cutscene can be found for E-102 Gamma that implies it would have been played after failing to complete Final Egg.
- Sonic's Light Speed Attack works differently in the demo and is the only upgrade implemented in the demo. Sonic kneels down instead of rolling and the player can press A to move or B to turn the move into a standard homing attack.
- Data inside the final game refers to unused levels such as a desert, jungle, and mushroom stage.
- There was a promotional image of Sky Chase with a fire-breathing mechanical dragon boss, but it's not present in the final product. It actually still exists within some versions of the game, but when hacked in all it does is follow the player without attacking, lacks proper animations, and nothing happens if you shoot it.
- In one demo of the game, using a cheating device to access the chao garden reveals a different chao releasing mechanism. Simply put, it's a button that, when pressed while a chao is placed in front of it, a grate opens up, it falls into it, and grinding and shredding sounds are heard. These sounds were possibly meant to replicate the Dreamcast processing noise and for the Dreamcast VMU device but seeing that the demo was not programmed for this feature, The screen on the mechanism says no data and there is no way to get the chao back.
- Knuckles' voice in the E3 1999 demo was different from the version in the final product. He had the same voice actor, however the voice direction was very different and more serious sounding. The lines were also slightly different. One of his lines ("Oh no!") was used in the final product, however in a separate cutscene. Oddly enough, some of these voices actually ended up used in Sonic Adventure DX, but only the ones that played outside of cutscenes.
Trivia / Sonic Adventure