Why is Luigi's Mansion 2 Called Luigi's Mansion Dark Moon in North America?
Luigi's Mansion 2 was released in 2013 for the Nintendo 3DS, and is the sequel to Luigi's Mansion on the Nintendo GameCube. The game has the player control Luigi as he explores abandoned mansions, captures hostile ghosts using his vacuum cleaner, and retrieves shards of the shattered Dark Moon.
The game was released as Luigi's Mansion 2 in Japan, Europe and Australasia. Interestingly, it was titled Luigi's Mansion Dark Moon in the North American release.
Spot the odd one out!
This isn't the first time that Nintendo of America have foregone using '2' in titles of games released in North America. Mother 2 for the SNES, originally released in Japan, was released in North America as EarthBound. The original Mother was never released in North America, so the title was changed from Mother 2 to avoid confusion about what it was a sequel to.
As another example, Baten Kaitos 2 for the Nintendo GameCube, originally released in Japan, was released in North America as Baten Kaitos Origins. This was probably to better reflect that Baten Kaitos Origin was a prequel to the original game.
So, why was Luigi's Mansion 2 renamed in North America? Nintendo didn't give an official reason, however we can speculate.
To better indicate that the original doesn't need to be played
Some people may have been reluctant to play Luigi's Mansion 2 without having played the original. However, playing the original would require a Nintendo GameCube, which is a console that's tricky to find and expensive to purchase. So, Nintendo of America likely dropped the number '2' from the title to make those who didn't play the original less hesitant to play Dark Moon.
To give the series a fresh start
The original game was released on the Nintendo GameCube twelve years before its sequel arrived on the Nintendo 3DS. The visuals, animations and gameplay have undergone significant improvements in Dark Moon, prompting Nintendo to frame the game as a series reboot, rather than a true sequel.
To give the game more of an 'identity'
Luigi's Mansion 2 is probably not the most inspiring or creative name. Dark Moon at least hints at the game's storyline.
However, these reasons don't explain why the game was only renamed in the North American release. Perhaps the Nintendo companies in Japan, Europe and Australasia are closely aligned, and Nintendo of America operates as more of a lone wolf? It'll be interesting to see whether the Dark Moon situation occurs for future North American releases.