Pokémon Picross (lost unfinished Game Boy Color game; 1999)
In spring of 1999, a new Pokémon-themed Picross game for the Game Boy Color, simply titled Pokémon Picross, was announced and widely advertised in Japanese magazines. It was cancelled for unknown reasons, however.
Notably, on April 1st 1999, a Japan-only downloadable SNES game (Picross NP Vol. 1) was released and featured twelve Pokémon puzzles. It is largely assumed that Pokémon Picross was either reworked into Picross NP Vol. 1, or whatever had been finished of the game was implemented into it. Additionally, a Pokémon-themed Picross game from the same developers was eventually released for the 3DS.