Complete every single cup with a first place unlocks new alternate Title Screens and unlocks the true ending credits.

Collect 10,000 Coins (Multiplayer gives players the total amount of Coins collected by all players during each race).

Use the Wii Handle for 50% of your most recent 100 stages.

Get at least one star (54 points or more) on every 150cc and Mirror Mode race.

Beat all of the Time Trials Staff Ghosts.

If you hold a specific button while selecting the Animal Crossing stage with A, you can actually choose what season you play on. These are: L for Spring R for Summer zL for Autumn zR for Winter.

There are 62 Unlockable Miiverse Stamps in Mario Kart 8: 30 character stamps and 32 track stamps.

Stamp	How to unlock
Character Stamp	Finish 1st in any Grand Prix with that character.
Track/Course Stamp	Beat the normal staff ghost time for track.

Earn a Gold Trophy for every Cup in the 150cc difficulty to unlock Mirror Mode. This mode lets you race in reversed versions of the existing Cups.

In Grand Prix mode, get first place on any Cup at any CCs and it will give one of the 14 Characters at random however you can not repeat the same cup with the same CCs.

In Grand Prix mode, get first place on any Cup in any engine class and you will be given one of 13 additional characters at random - however you can not repeat the same cup with the same engine class to earn more characters. The one exception to the above rule is the Mii character, the 14th unlockable character. He will be unlocked when you obtain first place in every Cup of a single engine class.

Press the accelerator button when "2" appears and hold it down for a rocket boost at the start of the race.

Vehicle parts are unlocked at random every time you get 50 coins. Once you reach 1000 coins total kart parts are unlocked every 100 coins. The only exceptions to this rule are the gold parts.