Win the Mushroom Cup at 50 cc to unlock Luigi's kart.
Win the Mushroom Cup at 100 cc to unlock Baby Luigi's kart.
Luigi's Mansion Battle Stage
Win the Mushroom cup at 150 cc to unlock this extra stage for multiplayer battle.
Win the Flower Cup at 50 cc to unlock Daisy's kart.
Win the Flower Cup at 100cc to unlock Waluigi's kart.
Win the Flower Cup at 150 cc to unlock Birdo's kart.
Win the Star Cup at 50cc.
Win the Special Cup at 50 cc.
Toad and Toadette Duo
Win the Special Cup at 100 cc to unlock these two characters.
Win the Mushroom, Flower, and Star Cups at 100cc.
All Cup Tour
Win all cups at 150cc.
Win the Star Cup at 150cc.
Win All Cup Tour at 150cc.
Win the Mushroom Cup on mirror mode.
Tilt Table Battle Stage
Win the Flower Cup on mirror mode.
Petey Piranha and King Boo
Win the Star Cup on mirror mode.
King Boo Kart
Win the Special Cup on mirror mode.
Win the All Cup Tour on mirror mode.
Get new title screen
Once you have recieved the gold trophy on Mushroom, Flower, Star, Special Cups, and The All Cup Tour on 50CC, 100CC, 150CC, and Mirror mode, like in Mario Kart 64 you will be rewarded with a new title screen featuring all of the racers.
Staff ghost racers
Beat these record times to unlock a staff ghost racer for each track:
Baby Park: 1:14.000
Bowser's Castle: 2:47.000
Daisy Cruiser: 1:55.000
Dino Dino Jungle: 2:03.000
DK Mountain: 2:15.000
Dry Dry Desert: 1:53.000
Luigi Circuit: 1:29.000
Mario Circuit: 1:44.000
Mushroom Bridge: 1:34.000
Mushroom City: 1:53.000
Peach Beach: 1:15.000
Rainbow Road: 3:19.000
Sherbet Land: 1:28.000
Waluigi Stadium: 2:02.000
Wario Colloseum: 2:24.000
Yoshi's Circuit: 2:02.000
These alternate routes, while not always faster than the normal route, may often give you more items than you'd normally get
Luigi Circuit: After you go off the first speed boost jump after the starting gate, if you hang a right there is a little path behind the chain chomp post. Before the second U-turn, there is another alternate route behind some pipes. I found it's not much use. These for Luigi Circuit only work in 100cc, 150cc.
Peach Beach: Before the first item row, there is a left turn that leads you into a pipe that shoots you out into a double item. Unfortunately, it does not help you any. Before the finish line, instead of going straight, turn left and go around the fountain. There are 2 double items, but it's longer to go that way.
Mushroom Bridge: Right after the starting line there is a ramp to the sharp right. Take it, go through a pipe, and you are shot out to receive a double item. This one is also longer than just going on the track. Also, after the first tunnel, there is a road to the left. Take it to avoid all the cars on this stretch of road and get an item.
Mario Circuit: In Mirror mode, use a mushroom to go behind the chain chomp through the grass. If you can do it right, it removes a few secs from your time. I found it best to use a light kart.
Bowsers Castle: In the big room where there is a bowser shooting fire balls instead of going around the U turn like part go straight forward in to a gap on the side of the track. Make sure you dont just drive into it you have to power slide to the right otherwise you will fall right off the other side
Boost after revival
At times you may be replanted on the track by a floating ally, usually after you've fallen off of the track. To get a free boost as he drops you, hit the accelerator just before you touch the ground. The timing is tricky, but it's worth the effort.
If a lightning bolt is used right when you get hit by a shell, banana, etc.-you wont get hurt. Same if you fall off the course.