- Not to be confused with Sonic the Hedgehog Extreme or the LCD game Sonic the Hedgehog Extreme Boarding.
Sonic X-treme is an unreleased platform game in the Sonic the Hedgehog series. It was originally developed by Sega for the Mega Drive/Genesis but was moved to the Sega 32X and eventually to the Sega Saturn and intended to be released around Christmas of 1996, but after many problems it was finally cancelled in 1997. Had it been finished, it would have been the first fully 3D Sonic game and the first original Sonic title developed for the Sega Saturn. This was the second Sonic game to be cancelled on the Sega Saturn, the other being Sonic Saturn.
Multiple storylines were considered during the game's production. The most known storyline was published in Electronic Gaming Monthly in 1995 as the "Red Shoe Chronicles". It involved new characters Professor Gazebo Boobowski and his daughter, Tiara, who are the keepers of the six magical Rings of Order, as well as the ancient art of Ring Smithing. Gazebo and Tiara fear that Dr. Robotnik is after the six Rings of Order, and call on Sonic to get the Rings before Robotnik can.
The final storyline that made it into the game itself was that Dr. Robotnik rebuilt his Death Egg larger than Sonic's planet, and its gravity was so powerful that it could rip planets from their orbits, but when Sonic was teleported, he found himself on a jungle planet surrounding the Death Egg, called "Jade Gully", with its residents, the "Mips", turning into Badniks. Sonic must free the captive Mips and destroy the Death Egg quickly.
Other storylines considered for the game included Sonic contracting Robotnik's "Doom" virus and being forced to find a cure for them both, Robotnik sidetracking Sonic during his attempted date with Tiara, a virtual world, and the shattering of the Master Emerald and the unleashing deadly six creatures.
Artwork of Tiara and her father have been released by the game's director Chris Senn along with various other details based on the game.
To further the traditional Sonic "go-anywhere-or-run-through" formula, every level was designed in a tube-like fashion; Sonic would be able to Spindash onto walls, thus changing the direction of gravity and the rotation of the level itself, much like the special stages in Knuckles' Chaotix. In addition, a fish-eye lens-styled camera was put into place so players could see more of their surroundings at any given time.
It is now known that at one point in the development process, there was a possibility for four playable characters. The characters planned were Knuckles the Echidna, Tiara Boobowski, Miles "Tails" Prower and Sonic the Hedgehog. Each character would also have had a unique gameplay style. Knuckles and Tiara would have had traditional-style play, having top-down and side-scrolling views respectively. Sonic had the fish-eye style levels, and Tails would play in first-person flight mode.
There were eight planned Zones: Jade Gully Zone (as pictured above), Crystal Frost Zone, Red Sands Zone, Galaxy Fortress Zone, Metal Blade Zone, Death Egg Zone, Candy Mountain, and Blue Ocean (became a test level). Sonic himself was to be equipped with a large set of new moves, including a spin slash, a ring throwing ability (early in development), a ring-powered shield, a sonic boom attack and a power ball. The spin slash move would have been cut out of the final version of the game due to being too similar to the spin dash move to attack.
Powerups were supposed to be contained in rotating spheres and included Shields. Shields were based on elemental powers (Metal, Rock, Lightning, Wind, Fire and Water) with each element being stronger than the first, making a "Circle of Power". The powers could be combined to make on of two "PowerShields":
- Elemental Circle of Power:
- Metal (cuts Rock)
- Rock (shields from Lightning)
- Lightning (electrifies Wind)
- Wind (extinguishes Fire)
- Fire (evaporates Water)
- Water (rusts Metal)
- (Metal - Lightning - Fire)
- (Rock - Wind - Water)
Other characters intended to be included in the game were Fang the Sniper and Metal Sonic, who would have been bosses in the final game and whose design and programming was actually finished by the time Sonic X-treme was cancelled.
Two bosses were described on the Chris Senn's Sonic X-treme Compendium website:
- Darkpool Gorilla Boss
- "Eventually, Sonic will make his way to the Boss zone - A huge cavern a thousand feet below ground. The walls of this huge spherical domain have been carved out by years of underground streams trickling slowly down its sides settling in a dark pool at the bottom. Several paths lead towards the center, where a tall, rocky pedestal juts up from the murky base. Atop this rests a huge hydraulic platform upon which a dark hunched figure stands dormant. Once Sonic reaches the overhanging straight pathway to the center platform, still leaving about 30-40 yards between, several things happen. First, a mechanical humming and drumming fills the thick, musty air. It is like some machine waking up after thousands of years of hibernation. A few indicator lights below the platform flash and come to life. The dark figure's eyes light up red and it suddenly stands erect. Stones and clumps of dirt crack and slide off of this Boss's massive cast-iron body. Twisting his upper torso from left to right a few times (as if waking up and stretching), the Darkpool Gorilla Boss sees Sonic and does a double take. Slamming the surface of the platform sends a quake right through the rickety bridge Sonic is standing on. Immediately, it starts to give way behind Sonic and the only way is to run forward to the frenzied Boss or fall to death. The hydraulic platform tilts according to weight change and Sonic's first test is to try and defeat the Rock Elemental's Boss suit On this teetering square. After defeating him, the platform sinks down on its piston base and activates two exit balls for Sonic to choose between."
- Mecha Mite Boss
- "Deep within the abandoned oil mines rests the Wind Element Keeper. Hibernating just below the oil lake, the Mecha Mite Boss is rudely awakened by our trespassing hedgehog and begins to lift itself from the black muck. This huge creature upsets the balance of rock and oil pockets and starts a chain reaction- As shards of sharp clay and rock fall into the shaking lake below. Oil oozes steadily out of reopened wounds in the cavern's walls. The whole earth shakes as Sonic's new challenge becomes apparent. Sonic is protected (for the moment) within a 6-tiered, cylindrical glass tower. On each floor, facing either North, South, East or West is a metal pipe that Sonic must spindash into to reach the floor above. Time is limited as the oil steadily rises on the outside and within this structure. An enemy or two will harass Sonic before the entrance to each pipe. Meanwhile, shaking and clawing its way to the top of the tower is the Mecha Mite, dripping with oil. Once Sonic reaches the top, the pipe he used crashes down into the now-paused muck. The Mecha Mite Boss attacks first by rising up and opening its immense three jaws to blow "oil wads" at Sonic. The Boss can also suck in huge pockets of air- Sonic must stand behind something or be pulled into the nasty, teeth-ridden jaws of Mecha Mite. Occasionally (and constantly before its death) the Boss spits out an appropriate enemy to attack Sonic. The final stage for this Boss is when it rises above the tower and holds onto the top with its claw appendages. Sonic must destroy these to send the Boss falling to its death."
Sonic X-treme was originally intended to be developed for several other game systems prior to the Sega Saturn. In its earliest conception, the game was set to be released on the Sega Genesis and later on the 32X, under the name Sonic Mars (based on the codename for the 32X, Sega Mars). However, it was quickly decided that the game would require much more powerful hardware to cope with the new engine, and for commercial reasons, the release of a Sonic game on the new Sega Saturn console was a necessity.
Sonic X-treme was eventually cancelled because of many internal problems. The game was being developed by Sega Technical Institute (STI), a U.S.-based developer that had worked on games such as Sonic the Hedgehog 2, Sonic Spinball and Comix Zone.
Game designer Christina "Chris" Coffin was hired by Sega and tasked with creating the separate boss level portions of the game that was suggested to use a different viewpoint from the main game. Ofer Alon and Chris Senn continued their work on the main game in parallel with Coffin's Sonic X-treme boss engine. Coffin developed all boss engine work on the Sonic Mars hardware prototype initially before it was decided that Sega needed to make a Sonic game for the Sega Saturn.
For the boss level engine, several modes such as top-down and side scrolling views were prototyped to create a more interesting view of the boss battle areas while still using the pre-rendered Sonic sprite assets used in the main game engine developed by Ofer. Ofer continued developing the main game editor tools and engine code on the Mac and PC. Development picked up again and it seemed the game's deadline for release would be met after all. From a code standpoint the boss engine and main game were basically two games developing at the same time that shared some global memory to remember game state and use a process called "executable chaining" to switch from the main game to boss levels and back.
The boss engine never used the NiGHTS engine, and never saw any code, tools or assistance from Sonic Team. Even one of AM1's own arcade teams from Japan that was transplanted to the offices of STI and developed Dynamite Deka (known as Die Hard Arcade) was not privileged with any such knowledge or special support. Teams had to pretty much fend for themselves, which was evidenced by almost nonexistent third-party tools and support network for Saturn at that time. A few months into Coffin's involvement in Sonic X-treme, the studio director Roger Hector showed Coffin a playable pre-release level of NiGHTS. Coffin fell in love with the game's look and feel of NiGHTS for Sonic X-treme's boss levels, which may be why Yuji Naka himself threatened to quit Sega several months later because he assumed the Sonic X-treme team had been given access to his game's source code and art; this was not the case (Naka is very well known to have had an extreme passion toward NiGHTS, one time claiming that one of the game endings had induced tears in his eyes). The boss level engine began to evolve into a game of its own using this new source of inspiration, trying to stay closer to its 2D roots by adopting a 3D but side-scrolling viewpoint seen in games like Klonoa, Pandemonium, and NiGHTS, which was more fluid and lent itself to the fast moving gameplay of previous Sonic titles. The new boss engine gameplay prototype adopted a more pastel color scheme and organic flow of the inspirational NiGHTS game, and this caused some divided opinions amongst team members that felt originality was being sacrificed.
At one point, Christina Coffin briefly toyed with the idea of Amy Rose as a playable character, so she modified all the sprites of Sonic to look like Amy, except for Spin Dash, Spin Slash, Spin Jump and running sprites. She threw rings as an attack, and since rings were your main source of energy, you were risking your life. Tiara had been long scrapped by this point, so Amy would have been the first female playable character in a main series Sonic game if the game were released. The music and sound effects used in the boss engine came from the Japanese version of Sonic the Hedgehog CD.
While Chris Senn and Ofer Alon tried porting the game to the Saturn, they encountered some problems, like the game running in 3-4 FPS with 4 colors and crashes. Point of View studio was recruited to continue technical development of the game, porting an older version of the game to the Saturn (now known as build v40) but encountering the same problems that Senn & Alon encountered. Some time after this, Ofer Alon was taken off the project. According to Senn, STI management viewed Alon as a maverick who did not follow company politics and did little to direct the other programmers. POV became the main developers, and to demonstrate to Ofer and Senn the reason for the drastic action, technical director Robert Morgan showed them a demo created by Point of View. Senn recalled, "They showed us the Sonic sprite we were already using floating in the upper-right of the screen, a checkerboard ground, a rotating shaded polygonal shape floating in the air and maybe a ring sprite animating. For all that we had created, to throw all that away for such nonsense. Amazing." After seeing this, Alon and Senn separated from POV & continued developing Sonic X-treme as a PC game. As known from the last leak of Sonic X-treme, POV made their own engine, with a completely different source code.
Sega of Japan meddled once again, as representatives came over to check on the game's progress. They were disappointed by the progress on the main game engine, as POV showed them a broken effort to port an older version of the engine (which is known now as v40), but were so impressed by the boss engine that they requested the entire game be made on that instead, as "Project Condor". By now the team was running short on men, and as Point of View had not gotten much farther than their initial demo, it all had fallen on the Sonic Xtreme Project Team to finish it up before the Christmas deadline so as to go up against both Super Mario 64 and Crash Bandicoot alongside NiGHTS. A major change in this project is replacing the pre-rendered Sonic sprite with a 3D model, made by Kunitake Aoki from Sega of Japan. Coffin, who had been working nonstop to get this project out, came down with pneumonia. Since Coffin was leading the technology end and creating the engine, the loss caused the project to be indefinitely delayed and Mike Wallis informed management that the team could not continue and the game would not be released in time for Christmas. The project was officially cancelled. Sega of America decided to discontinue both the Saturn and PC versions and switched to an alternative project: a Saturn port of Sonic 3D Blast.
The first contribution related to Sonic X-treme was in 1999, when Ross Harris contributed almost every sprite of Sonic used in X-treme.
A disc of a test engine of X-treme exists. A copy was sold at auction to an anonymous collector in September 2005, and a high-quality gameplay video was expected to be released by the end of the year. An animated GIF image of the gameplay was released to the community. The disk image was finally leaked on 17 July 2007. This prototype is actually Sonic X-treme early in it's conversion to Project Condor. An exclusive feature in this prototypes (and all other versions of Chris Coffin's boss engine) were blue crystals that throw you to the sky when touched. This prototype is often called "the 718 prototype", since "SONIC J.G 7.18" was written on its disk (which imply that the prototype was made in 18 July 1996). The music played in the prototype is "Quartz Quadrant Good Future" from the Japanese version of Sonic CD.
In early January 2006, the game's director Chris Senn opened a forum based on the game on his own message board, and began revealing large amounts of the game's development history to the public, including videos of early attempts, a mockup of Tiara's gameplay, concept art of Tiara, and more. Furthermore, he posted a large amount of previously unreleased concept music related to the title, and was given permission by Hirokazu Yasuhara (the level designer for the majority of the original 16-bit Sonic titles, including the first one) to post level designs that were going to be put in the game. Most of this information was posted on the Sonic X-treme Compendium website (SXC), which officially went online 5 April 2006.
The same year, a Sega Saturn SDK was leaked online, and contained models from the Sega Saturn version of Wipeout, a Saturn tech demo of Virtua Fighter 3 (which was released on arcades and Dreamcast eventually) and models from the Project Condor (the entire Sonic X-treme rebuilt with the boss engine) era of the Sonic X-treme, which are a Green Hill Zone Ground model (basically it's the same model from the 718 prototype with a different texture), a monitor model with a picture of Sonic and Amy on it from Sonic CD, the Sonic model from the Project Condor era & the 3D model for Metal Sonic that was used in the boss battle.
In 2009, a big package called PackageX was released. The package included textures and levels from Sonic X-treme, along with a level viewer to see and explore the levels in an unplayable format. There were two exclusive characters in this package: Chaz and Gabby, but Chris Senn confirmed they were used as test art in a personal side project that was using Sonic X-treme's engine.
In November 2014, a member from ASSEMbler Games called "Jollyroger" found material of Point of View studio, which included some unreleased betas for their games. In the material, there were two prototypes of Sonic X-treme, along with their levels that were used in the E3 trailer, both made by Chris Senn and Ofer Alon. The first one, v37, doesn't have fisheye and was played on the PC, while the second one is a both a PC game and a Saturn ISO that has fisheye. The Saturn version of v40 is a working continuation of POV's broken effort to port an older engine of the game, which previously ran at 3-4 FPS, and has only 2 frames of animation for each sprite, unlike the PC version. Jollyroger also found their level editors as well. The prototypes require a nVidia NV1 video card & SDK & Windows 95 to work, so Jollyroger is converting them to render in OpenGL. Meanwhile, only one level of build v37 was released. The level is the Jade Gully level from the E3 trailer. Another level that was released, is a fisheye-lens level from v40. An exclusive feature in these betas is that Sonic could do an infinite jump, maybe for debugging the level. Exclusively for v37, the player can use the "World Rotation" gameplay mechanic, by spinning into walls and slopes. Jollyroger also has the level editor for v53 (the New Worlds Demo version), but not the engine itself. In October 2015, all the v37 levels were release.
Another prototype that was found and released by Jollyroger is POV's version, dated 14 July 1996, which uses a completely different source code and has physics similar to the first three Sonic games. In this version, Sonic explores Jade Gully Zone act 2, and the player can go to Debug Mode by pressing Start+C buttons on the Saturn. Unlike the previous prototypes, the player can collect rings and defeat enemies, but you can also get hurt by enemies and Rings will fly out.
Currently, the only Saturn emulators that can run Sonic X-treme v40 are "SSF" and "Satourne", when the latter is the only one that managed to run it in 30-60 FPS, unlike SSF, which runs it in 30 FPS and real hardware, which can run it in 15-20 FPS. The POV build runs perfectly on Satourne, SSF and real hardware, but has graphical glitches on Yabause.
Senn later started Project S, an effort to complete the game unofficially. However, he later stated that it will be an original fan game heavily inspired by Sonic X-treme, rather than a straight resumption of the unfinished project. On 12 January 2010, Senn announced that Project S was cancelled.
"Many people worked very hard throughout the project’s three-year and three-month life cycle. Making any product is extremely difficult, and Project S was no exception. Working for free and online with a wide range of experience, skillsets, availability and dedication just didn’t work out for the team responsible for Project S. The hope is that the successes the team earned along the way are complemented by lessons learned that, unfortunately, led to our collective inability to reach a public release." At one point, there was an article on the gaming site GameSpot referring to a possible release of a "Project S" for the PSP; however, the released game turned out to be Sonic Rivals.
- Sonic X-treme's level editor, engine and internal name are called SonicBoom and SONCBOOM.
- The game was originally based on the Saturday morning cartoon series while it was still under the title Sonic Mars and was going to include the Freedom Fighters. However, they and all other elements from the TV series were dropped when the project became Sonic X-Treme.
- The 1996 Christmas television special Sonic Christmas Blast was originally titled An X-Tremely Sonic Christmas, apparently with the intention of promoting Sonic X-Treme. The delay of X-Treme forced the special to be given a new title similar to Sonic 3D Blast, which came out on time.
- If this game was released, it would have been both Fang the Sniper and Amy Rose's second 3D appearances, the first being Sonic the Fighters.
- In the 718 prototype, there are two Easter eggs: The first one is if you disable some layers, you can see the ground texture from the Metal Sonic boss battle from Metal Blade. The second one is that if you pause the game and press "C" button, you get a game over screen, and then, the game resets. The game over screen uses the game over theme from the Japanese version of Sonic CD.
- The story about "Rings of Order" was made up for a magazine while the real plot was in progress.
- An ice cream bar, radio and cassette player ware made to promote the game, but were discontinued due to its cancellation. However, it was later released in normal Sonic the Hedgehog packaging.
- Despite the fact Sonic X-treme was cancelled, many elements were later carried over to other games such as Sonic Adventure, Sonic Colors, and most noticeably Sonic Lost World which reuses an unused plot and some gameplay mechanics from Sonic X-treme, as well as the level structures looking quite similar to each other.
- Sega Saturn version could be called "Sonic Ringworlds", also names "Sonic Bluestreak" and "SuperSonic" were briefly considered.
- This would have been the first main series game where Amy Rose would be playable had it been released.
- A port for the Game.com was in the works, however it might have been a prototype for Sonic Jam.
The conceptual soundtrack by Chris Senn was posted on Sonic X-treme Compendium, Chris Senn's website dedicated to Sonic X-treme development. It was created to inspire Howard Drossin (Sonic the Hedgehog Spinball composer) who would make the official soundtrack.
|x01 Magmatropolis||Chris Senn||1:29|
|x02 Tombs-n-Traps||Chris Senn||1:00|
|x03 Volcano X||Chris Senn||1:30|
|x04 Mummy Madness||Chris Senn||1:01|
|x05 Pharoah Den||Chris Senn||1:30|
|x06 DiscoPyre||Chris Senn||1:14|
|x07 Jewel Keeper||Chris Senn||1:42|
|x08 Islam Prophet||Chris Senn||0:56|
|x09 Giza Speedway||Chris Senn||1:04|
|x10 Crimson Crypt||Chris Senn||1:01|
|x11 Pyro Pools||Chris Senn||0:39|
|x12 Gaurdian Sphinx||Chris Senn||1:16|
|x13 Darkroads||Chris Senn||1:00|
|x14 Necropolis||Chris Senn||0:54|
|x15 Nightmare Bridge||Chris Senn||0:56|
|x16 Black Harbor||Chris Senn||0:55|
|x17 Smog Tower||Chris Senn||1:37|
|x18 Concrete Pits||Chris Senn||1:01|
|x19 Streets of Gold||Chris Senn||1:36|
|x20 Shadow Market||Chris Senn||0:50|
|x21 Underdrowned||Chris Senn||1:00|
|x22 BigBadWolf||Chris Senn||0:51|
|x23 Assault Station||Chris Senn||1:24|
|x24 Sewer Shock||Chris Senn||0:41|
|x25 Spiral Staircase||Chris Senn||0:40|
|x26 Proving Grounds||Chris Senn||1:04|
|x27 Mesh Machine||Chris Senn||1:02|
|x28 Technoweb||Chris Senn||0:40|
|x29 Iron Program||Chris Senn||1:15|
|x30 Eery Descent||Chris Senn||0:49|
|x31 Factory Robo||Chris Senn||0:48|
|x32 MegaBase Control||Chris Senn||0:51|
|x33 Titan Tank||Chris Senn||1:32|
|x34 Shiver Plains||Chris Senn||1:01|
|x35 Cryogenesis||Chris Senn||1:02|
|x36 Prism Chorus||Chris Senn||0:40|
|x37 Frozen Falls||Chris Senn||0:49|
|x38 Borealis||Chris Senn||1:34|
|x40 Murk Trench||0:32|
|x42 Coral Realm||0:45|
|x43 Pearl Mountain||1:24|
|x45 Petroleum Proteus||1:09|
|x46 Ultra EelecTrick||0:59|
|x47 Emerald Clouds||Chris Senn||0:57|
|x48 Bamboo Transit||Chris Senn||1:03|
|x49 Floating Stones||Chris Senn||1:13|
|x50 Wolf Den||Chris Senn||0:56|
|x51 Skyhive||Chris Senn||0:49|
|x52 Royal Mobius||Chris Senn||0:54|
|x53 Options||Chris Senn||0:45|
|x54 Credits||Chris Senn||1:03|
|x55 PC Demo||Chris Senn||1:14|
|x56 Lost Boss||Chris Senn||1:22|
|x99 Base Jump||Chris Senn||1:49|
|x99 Castle of Light||Chris Senn||1:36|
|x99 Circuit Centerfold||Chris Senn||3:12|
|x99 Cortisone||Chris Senn||1:36|
|x99 Crystal Valley||Chris Senn||2:22|
|x99 Death||Chris Senn||0:07|
|x99 Destructor||Chris Senn||2:41|
|x99 Disciples||Chris Senn||3:18|
|x99 FantaSea||Chris Senn||3:55|
|x99 Mobius||Chris Senn||2:20|
|x99 Pickup1||Chris Senn||0:06|
|x99 Quake Caverns||Chris Senn||2:28|
|x99 Rebirth||Chris Senn||3:20|
|x99 Shield of Discovery||Chris Senn||5:41|
|x99 Spirit Gates||Chris Senn||3:17|
|x99 Tarantulas In The Grass||Chris Senn||3:04|
|x99 Teal Trouble||Chris Senn||1:55|
|x99 Tile Tracks||Chris Senn||2:54|
|x99 Zone Done||Chris Senn||0:07|
|Space Queens (Promo)||Chris Senn||2:32|
|Space Queens (Extended)||Chris Senn||3:18|
- Chris Senn (19 January 2006). Knuckles!. Senntient. Archived from the original on 18 July 2011.
- Sonic X-treme Compendium FAQ. "A: The powerups were to be contained in a rotating sphere, with Sonic having to spindash or land on one to get the power up.
Shields were based around a concept called "Elements". Elements represented the six powers that Sonic could unlock. There was a hierarchy of power whereby each Element was stronger than the next with the last Element being stronger than the first, thus making a Circle of Power. Every other Element could be combined together to make one of two special "PowerShields".
Elemental Circle of Power:
- Metal (cuts Rock)
- Rock (shields from Lightning)
- Lightning (electrifies Wind)
- Wind (extinguishes Fire)
- Fire (evaporates Water)
- Water (rusts Metal)"
- (Metal - Lightning - Fire)
- (Rock - Wind - Water)
- Chris Senn (18 April 2006). The Sonic X-Treme File Archive: home > boss. Project Sonic. Archived from the original on 14 October 2008.
- Ashley Davis (19 November 2008). What could have been: Sonic X-treme. Destructoid. Archived from the original on 11 November 2020.
- Sonic X-treme Compendium FAQ. "A: The "Rings of Order" was part of a simple story generated for a news article in a magazine at a point when the real game story was in progress. The magazine needed something to print and the team wasn't ready with a final story. The idea behind it leveraged the concept that there were magical rings, special rings, that coincided with the Chaos Emeralds that provided order to the Universe when kept together. Using this as a setup, any number of things could happen - not the least of which was Robotnik stealing them and Sonic trying to "restore order" by replacing them."
- AM/FM Radio Promo For UNRELEASED Sega Saturn Game SONIC X-TREME! NEW! Hedgehog. eBay (20 November 2020). Archived from the original on 26 November 2020.
- Vintage Sega Sonic the hedgehog Xtreme portable stereo cassette tape player. eBay (2 August 2017). Archived from the original on 26 November 2020.
- Sonic X-treme Compendium FAQ. "A: The project went through many name changes and considered others, usually corresponding to platform changes mandated from management or the introduction of drastically new technology. The names that were considered or actually given to the project included:
- Sonic 16 (Genesis)
- SonicMars (32X)
- Sonic32X (32X)
- Sonic Saturn (Saturn)
- Sonic Ringworlds (Saturn)
- SonicBOOM (Saturn / nVidia08)
- Sonic Xtreme (Saturn)
- SonicPC (PC)
- Sonic Bluestreak (briefly considered)
- SuperSonic (briefly considered)"
- Chris Senn (24 September 2007). The Sonic X-Treme File Archive:home > music. Project Sonic. Archived from the original on 14 October 2008.
- Sonic X-treme Compendium FAQ. "A: Christian Senn created the conceptual music prior to and all the way through development of the game. This music served to inspire creative discussions, to dream up levels and gameplay, enemies and bosses, and was intended to serve as a brainstorm starting block for Howard Drossin. The idea was to enlist Howard's sound and music expertise once the game was developed enough, play any relevant conceptual music, and then let him create whatever music or style he thought would be appropriate for the game."
- Sonic X-treme Compendium (SXC), a website by Chris Senn that includes detailed looks of what Sonic X-Treme would have been (archived by the )
- Sonic X-treme archives including a backup of SXC (archived by the )
- Sonic Xtreme - The Unreleased Sonic Game's History Part 1
- Sonic Xtreme - The Unreleased Sonic Game's History Part 2
- Sonic Xtreme - The Unreleased Sonic Game's History Part 3