Play Grand Prix on Higher Difficulties
ARMS’ Grand Prix mode can be pretty rage-inducing on higher difficulties, especially if you’re just starting out in the game. However, increasing the difficulty also increases the number of coins you earn for each victory, plus an additional one for any perfect matches. This will allow you to build up your coin pool at a much faster rate, allowing you to play the mini game more frequently to unlock more customization options.
While the Party matches will also reward you with coins (whether you win or lose), the process will go by a lot quicker if you increase the difficulty level for Grand Prix instead. I recommend playing through Grand Prix at levels 1 or 2 if you’re still new at the game, and haven’t fully mastered the controls yet. If you’re looking to farm coins, level 4 is a good place to start. Any higher than that, and you’ll be faced with some seriously challenging AI behavior, and it’ll become too much of a grind at that point.