You can obtain Mario Kart World’s unlockables through various methods, so here's how to get new stickers, karts, characters, and costumes.

Characters have different unlock methods in Mario Kart World. Some characters require you to win at a certain cup, whereas others are random unlocks from using the Kamek item in races. For the cups, you’ll need to play and complete the cup in the Grand Prix, it doesn’t matter if you place or not.

To unlock Mirror Mode you are going to need to put in some work, as it requires you to play through all of the cups--including the unlockable Special Cup, which features Rainbow Road --both Circuit and Knockout, in addition to earning some rewards in the free roam mode.