As an updated re-release, Mario Kart 8 Deluxe comes with a lot of content available at the start, but there are still a few hidden unlockables.
Mario Kart 8: All Gold Items & Other Unlockables & How To Get Them
Unlockables - Mario Kart 8 Guide - IGN
Mario Kart 8 Deluxe Unlockables Guide
Mario Kart 8 Deluxe: The FASTEST Way to Earn Coins & Unlock Kart Parts (10 Coins Per Minute Trick!)
Mario Kart 8: Prima Official Game Guide by Musa, Alex , paperback 9780804163286
Mario Kart 8 Deluxe Unlockables, Characters and Tracks - Gold Mario and Gold Kart
How to UNLOCK GOLD Mario & Parts in Mario Kart 8 Deluxe
Mart Kart 8 Deluxe Beginner's Guide
How to Unlock Mario Kart Cups and Characters: 11 Steps
Mario Kart 8 Deluxe Unlockables Guide
Mario Kart 8 Deluxe: How to unlock everything