Panel de Pon 64 (lost build of unreleased Nintendo 64 sequel to Super Famicom puzzle game; 1999-2000)
Panel de Pon 64 (パネルでポン64 in Japanese) was an unreleased Nintendo 64 puzzle game developed by Intelligent Systems and planned to be published by Nintendo. It was intended to be the sequel to the 1995 Super Famicom game Panel de Pon (released outside of Japan on the SNES as Tetris Attack).
The existence of Panel de Pon 64 has been rumored several times on different message boards from 2009-2013. But no screenshots or any official info has surfaced online at the time, nor was it shown at game conventions. It was often debated whether it was supposed to be a tech demo that was testing the N64 hardware or if it was actually going to be released. The game would eventually be canceled and be instead reworked into Pokémon Puzzle League which would be released in 2001 exclusively in North America. The GameBoy Color version of Pokémon Puzzle Challenge would include unused assets of the characters from Panel de Pon hidden within the ROM, implying that it was also originally going to be a Panel de Pon game under the name Panel de Pon GB and would have released alongside the N64 release, as they used the redesigns from that version.
It's presumed that Panel de Pon was reworked into Pokémon Puzzle League due to the latter being more gender-friendly than the former and would have a higher chance of selling more than a game with a lead and most of its cast being girls which would have been risky at that time.
It was suspected that the version of Panel de Pon used in the Japan-exclusive 2003 GameCube puzzle compilation Nintendo Puzzle Collection, was the unreleased N64 game as the Dr. Mario port in the collection was identical to Dr. Mario 64 which was only released in America in 2001. In July 2020, YouTube user Gamers Manuel discovered a prototype cartridge of the Nintendo 64 version, and uploaded the video to his channel showcasing it. The unreleased game showcased was similar to some extent but was not the version released on Nintendo Puzzle Collection with its different title screen, and the Nintendo logo splash screen, which says "Pre Beta Version 79".
As of 2023, the game has yet to be dumped online, despite the owner being interested in dumping it.