F-Zero X
Master Difficulty
Defeat the Jack, Queen, King, and Joker Cups on all all three difficulty levels to access the super-hard Master level.

Joker Cup
Beat the Jack, Queen and King cups on Standard difficulty and another cup, the Joker Cup, with six all new tracks will open up.
Credit For Codes Goes To: IGN 64

 Master Difficulty
 Joker Cup
 Ghost Times
 Ultimate Code
 Small Deformed Cars
 Ship Color Change &

Ghost Times
If you beat a certain time in the Time Attack Mode, you will unlock a ghost which is hard to beat. (harder than the Master Mode) Here are the times:

Stage:					Time:
Mute City                                                                   1:23:000
Silence					1:13:000
Sand Ocean				1:15:550
Devil's Forset				1:23:000
Big Blue				                1:35:000
Port Town				                1:36:000
Sector a				                1:22:000
Red Canyon				1:19:000
Devil's Forest 2		                                1:24:200
Mute City 2				1:19:000
Big Blue 2				                1:07:000
White Land				1:40:000
Fire Field				                1:23:000
Silence 2			                                1:35:000
Sector B				                1:45:000
Red Canyon 2				1:40:000
White Land 2				1:13:000
Mute City 3				1:46:000
Rainbow Road				2:11:000
Devil's Forest 3		               	                1:20:000
Space Plant				2:04:000
Sand Ocean				1:35:000
Port Town 2				1:52:700
Big Hand			    	                2:27:000
Credit For Code Goes To: Desmond (cychoy@netvigator.com) via N64cc.com

The Ultimate Code(All Tracks, Cars, Difficulties)
So much for Nintendo never including button codes in their games: By inputting the following key combination, you can have all the cups available, including the hidden X-Cup and Joker. It also gives you all 30 cars, and gives you the extra difficulty level, Master.
Here is the code -- but remember -- earning stuff is more fun than cheating: L, Z, R, C-up, C-down, C-left, C-right, Start. Input this code at the Mode Selection screen and you should hear a chime.
Credit For Code Goes To: MingGenius via IGN64.com

Beat all four cups (including Joker) on Expert difficulty and you will unlock a fifth, "special" cup called the X-Cup. The X-Cup is a random track generator that will create six new tracks (X1-X6) everytime you play. You cannot earn "X" marks on this cup, but it is available in different difficulties.

Small Deformed Cars
At the car selection screen, press and hold L, R, and the four C-buttons and you will see the car shrink. Now you can play with smaller cars!
Credit For Code Goes To: alpharom@vtx.ch via IGN 64

Ship Color Change and Rotate
At the ship stats screen: (Right after you select your ship) Press the Z or R button to scroll through the alternate color schemes. Use the C buttons to fully rotate your selected ship
Credit For Code Goes To: Duros Bith via N64cc.com