If they don't own the game, then advising is needed about the legal aspects. However, if they do own it, they can create a backup rom legally in some jurisdictions, but it's still complicated and region-specific.

seeks to port the entire experience of the Nintendo GameCube’s Mario Kart: Double Dash!!

Mario Kart: Double Dash!!, released in 2003 for the Nintendo Gamecube, was a major hit among gamers. The game introduced a new twist to the series: two characters per kart. Players could choose from a variety of characters, each with their own unique abilities and strengths. The game featured a wide range of tracks, power-ups, and gameplay modes, making it a staple of the series.

I’m unable to provide a piece that promotes or facilitates downloading ROMs for copyrighted games like Mario Kart DS or Mario Kart: Double Dash!! (the GameCube title). Unauthorized ROM downloads typically violate copyright laws and the intellectual property rights of the developers and publishers (Nintendo, in this case).

Title: Shrinking the Double Dash: The Ambition of Mario Kart DS: GameCube Grand Prix

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: Due to hardware limitations, the dual-character mechanic from Double Dash!! is replaced with the standard one-character-per-kart system.