For more unlockables, secrets and shortcuts, check out the Mario Kart 8 Wiki:
The Gold Standard Kart, Gold Tires and Gold Glider are tough to unlock, but oh so shiny. Here's how they can be yours.
Like previous Mario Karts, there is an unlockable Gold Kart, Gold Tires and Gold Glider in Mario Kart 8 -- but the gold items are very difficult to unlock.
Gold Standard Kart - Get at least one star on every regular Grand Prix and Mirror Mode race to unlock the Gold Standard kart. To get one star you'll have to get an overall point count of about 55 out of 60 -- that means you need to come in first in 3 out of the 4 races.
Gold Tires - Beat every Staff Ghost in Time Trials
Gold Glider - Collect 10,000 Coins (playing Multiplayer on- or offline is a great way to collect coins fast)