WWF No Mercy (lost Game Boy Color games based on Nintendo 64 wrestling game; 2000)
WWF No Mercy was a video game released for the Nintendo 64 in 2000 and is considered one of the greatest games for the platform as well as one of the greatest wrestling games of all time. However, it was meant to have an alternative version for the Game Boy Color. This version, however, was canceled after a troubled development history with changes to the game's developers. There were actually two versions of the game developed by two different developers with neither of them surviving.
The game was originally in development along with the Nintendo 64 counterpart being developed by Aki/Asmik, a first for the series on the Game Boy Color . However, during development, it changed to being developed under Natsume, the developer of the previous WWF Game Boy Color game, WWF Wrestlemania 2000
Interactivity with Nintendo 64 version
The Nintendo 64 version was planned to have compatibility with the Game Boy Color version as an unused championship path (the main single player mode of the game) exists in the code for N64 version of the game which can be accessed using a GameShark cheat device (although unfinished). Beating this championship mode allows you to transfer your created wrestler from the Game Boy Color version to the N64 version of the game.  The IGN page for No Mercy claims "Transfer Pak links with two GBC-only WWF games." What this second game is unknown. It should be noted that there were multiple claims to what the transfer pack would unlock. Originally it was said it would unlock hidden items and that it would unlock hidden features in the N64 game. Along with being able to transfer your points to spend in the Smackdown Hotel (in-game store) to unlock characters and moves from GBC to N64.  It is possible all these features were in fact planned.
Having a create a wrestler is a feature that was not in WWF Wrestlemania 2000 and would have been new to the game. It is unknown how detailed this mode would have been or what exactly it would entail. It may have also had points to unlock things in an in-game store as moving points between versions was a feature mentioned.
While footage or screenshots have never been found for the game, it can be assumed that it would play like WWF Wrestlemania 2000 for the GBC. According to an IGN article on the port: "originally to be designed by Aki, the title then went back to the designers of the lackluster WWF Wrestlemania 2000 on the old engine for a quick conversion" implying that it would've been the same as Wrestlemania 2000 gameplay wise but having different wrestlers.
The game was canceled after the game missed the holiday 2000 deadline with no footage or screenshots ever being released of either the Natsume or Aki version of the game.
It is unknown if anyone has access to the game in any form. There is an unsourced rumour on Wikipedia that screenshots of this version of the game were deleted from the internet at the request of Natsume  This is the only known information on screenshots or footage of the canceled game.
- AJ Styles vs Kenny Omega (lost footage of professional wrestling match; 2006)
- Alberto Del Rio vs CM Punk vs Dolph Ziggler vs Jack Swagger vs John Cena (partially found master tape footage of untelevised Hell in a Cell match; 2011)
- Awesome Kong vs Melissa Anderson (lost footage of professional wrestling match; 2009)
- Bill Longson vs Whipper Billy Watson (lost footage of professional wrestling match; 1947)
- Blood Circus (partially found Santo Gold film; 1985)
- Braden Walker's "Knock Knock" promo (lost original pre-tapes of WWE backstage segment; 2008)
- Bradshaw vs Christian (lost footage of professional wrestling match; 2001)
- Bret Hart-Hulk Hogan photoshoot (lost professional wrestling promotional photos; 1993)
- Bret Hart vs Tom Magee (found untelevised professional wrestling match; 1986)
- Catch-As-Catch-Can Wrestling (lost early BBC televised professional wrestling matches; 1938-1939; 1946-1947)
- Celebrity Wrestling (partially found ITV professional wrestling reality show; 2005)
- Chowdaheads (partially found unaired professional wrestling cartoon show; 1999)
- Collision in Korea (found professional wrestling event in North Korea; 1995)
- Collision in Korea wrestler sketches (lost North Korean pencil sketch portraits of professional wrestlers; 1995)
- Cultaholic (found debut video of professional wrestling YouTube channel; 2017)
- ECW Anarchy Rulz (lost build of cancelled Nintendo 64 port of professional wrestling game; existence unconfirmed; 2000)
- ECW at E3 2000 (partially found footage of professional wrestling at gaming trade event; 2000)
- ECW Hardcore TV final episodes (lost episodes of Professional Wrestling Show; 2001)
- FMW at E3 2000 (partially found footage of professional wrestling at gaming trade event; 2000)
- The Game (partially found Disturbed cover of professional wrestling theme song; mid 2000s)
- GFW Amped (partially found unaired professional wrestling show; 2015)
- The Giant's moonsault (lost footage of professional wrestling move; existence unconfirmed; 1990s)
- Girls Gone Wild: Live from Spring Break (found WWE/Girls Gone Wild crossover special; 2003)
- GLOW (lost unfinished final season of Netflix comedy-drama series; 2019-2020)
- Goldberg's pre-television debut matches (lost footage of professional wrestling dark matches; 1997)
- Gotch-Hackenschmidt Match Film (lost world championship match; 1908)
- Gotch-Hackenschmidt Match Film (lost world championship match; 1911)
- Jake "The Snake" Roberts DDTs Hulk Hogan (lost Snake Pit segment; 1986)
- Johnny Gargano vs Velveteen Dream (lost footage of alternate finish to professional wrestling match; 2019)
- Kurt Angle vs Owen Hart (lost footage of professional wrestling match; 1999)
- The Last Battle of Atlanta (found untelevised professional wrestling steel cage match; 1983)
- Lita's training matches (partially found training videos of professional wrestler; late 1990s-2000)
- Low Ki & Mercury vs Ric Blade & TCK (partially lost footage of hardcore wrestling tag team match; 2000)
- Mark Jindrak in Evolution (partially found unaired vignettes of professional wrestling stable; 2003)
- Pat Tanaka vs Rocco Rock (lost footage of "Body Count" professional wrestling match; 1993)
- "Plane Ride From Hell" (lost photographs of drunk wrestler incidents; 2002)
- Radio WWF (lost professional wrestling radio show; 1993-1994; late 1990s-2000)
- Screwed: The Bret Hart Story (lost unfinished wrestling documentary film; 2005)
- Sex University (lost WWE webshow; 2006)
- Shin Nihon Pro Wrestling Gekitou Densetsu (lost build of unreleased Virtual Boy wrestling game; 1995)
- Strange Kentucky People (lost recording of Chris Jericho "tribute"; 1994)
- TNA Impact! 2 (lost build of unfinished professional wrestling game; 2009)
- WCW 2000 (lost work on unfinished PlayStation 2 game; 2000)
- WCW All Nighter (partially lost professional wrestling compilation show; 1994-1995)
- WCW Classics (partially found professional wrestling compilation show; 2000-2001)
- WCW Internet-only Special Events and PPVs (lost audio streams; 1997-1998)
- WCW/nWo Live (lost build of cancelled PlayStation professional wrestling game; 1998)
- WWE 24x7 (lost professional wrestling compilation show; 2007)
- WWE Brawl (lost build of cancelled fighting game based on professional wrestling; 2012)
- WWE Crush Hour (lost build of cancelled Xbox port of vehicular combat game; 2002)
- WWE SmackDown vs Raw Online (lost build of cancelled online professional wrestling PC game; 2010-2011)
- WWE Wrestlemania 36 (lost footage of alternate finishes to professional wrestling matches; 2020)
- WWF Attitude (lost professional wrestling recap show; 2001-2002)
- WWF Backlash (non-existent unfinished Nintendo 64 professional wrestling game; 2001)
- WWF Excess (partially found professional wrestling talk show; 2001-2002)
- WWF In Your House 8: Beware Of Dog (partially found untelevised professional wrestling matches; 1996)
- WWF Livewire (partially found professional wrestling recap and talk show; 1996-2001)
- WWF Shotgun (partially found July to December season of syndicated wrestling show; 1997)
- WWF Xperience (found pay-per-view event footage; 1996)
- IGN Article with confirmation of the game developed by Aki.
- IGN article where it is confirmed it was changed to Natsume and the game's cancellation.
- The Cutting Room Floor article that goes over the code for transfer pack championship path in the N64 game.
- Gamespot article where the transfer pack details are talked about.
- Wikipedia Article with this unsourced claim