Copied from BootlegGames Wiki:
Harry Potter 2 is a shoot 'em up game for the Game Boy Color released in 2002.
Despite the name, its plot is loosely based on that of Harry Potter & the Philosopher's Stone, with graphics in the introductory cutscene taken from the official Game Boy Advance game of the same name.
This game shows signs of being developed by Vast Fame - leftover menu graphics from Zook Hero 2 are in the ROM. However, unlike other Vast Fame games, it does not use the Mega Man V sound engine; the sound engine, and all music in the game, is instead stolen from the Game Boy version of Konami's Parodius Da!.
The original version, which has a 2002 copyright date, is called "Harry Potter 3: 神奇の光輪" (Shen Qi Zhi Guang Lun), which roughly translates to "Harry Potter 3: Mystical Halo". It is also called "Harry potter 3: mystical realm", which comes from a review or talk about the harry potter movies.
The game is a horizontal shoot 'em up featuring Harry Potter flying on a broomstick - there are four different weapons, each of which can be upgraded twice by collecting the same type of power-up again.