Jump Higher:
The good news is that when you are going over a jump all you have to do is press R to jump higher, the bad news is that it requires precise timing which isn't easy to do and may take you a while before you get the hang of it.

Save Time at Sandy Pits:
Don't get slowed down by the sandy pits on curves, just use a mushroom to cross over them.

Unlock Alternate Title Screen:
Finish all classes with Gold Trophies on all cups

Unlock Daisy:
Get a Gold Trophy on every cup in Retro Grand Prix on 50cc

Unlock Dry Bones:
Get a Gold Trophy on every cup in Nitro Grand Prix on 50cc

Unlock Waluigi:
Get a Gold Trophy on every cup in Retro Grand Prix on 100cc

Unlock 3rd Kart for All characters:
Get a Gold Trophy on every cup in Nitro Grand Prix on 100cc

Select from 7 Karts for each character:
Get a gold trophy in every cup in Nitro Grand Prix on 150cc

Unlock 150cc Mirror Mode:
Finish 150cc Retro Class with Gold trophies on every Cup

Select from any Kart for each character:
Get a gold trophy in every cup in Retro Grand Prix on 150cc Mirror mode

Unlock R.O.B. As a Racer:
Finish 150cc Mirror Mode Nitro Class with Gold Trophies on all Cups

Unlock 'Mission 7' in Mission Mode:
Get a 1-Star ranking on All levels of every mission in mission levels 1-6

Unlock Lightning Cup:
Get Gold on Leaf Cup

Unlock Special Cup:
Get Gold on Star Cup

Unlock Star Cup:
Get Gold on Mushroom Cup and Flower Cup

Unlock Leaf Cup:
Get Gold on Shell Cup and Banana Cup