There are no known unreleased games for the Pokémon Mini.
Some games, however, did not see originally planned releases in other regions. "Pokémon Puzzle Collection Vol. 2" and "Pokémon Mini Shock Tetris" were both rated by the ESRB, so there were finished but unreleased US versions. The european release of "Pokémon Tetris" happened in extremely low numbers, leading some to consider it "unreleased" in Europe.