Spyro The Dragon demo:
At the main menu, press Up, Up, Down, Down, Left, Right, Left, Right, Square.
On the level of Bagdad in the morning, finish the level to open time trial, and get the long spin ability. Get into the level, and start time trial mode. About 10-30 sec after there will be 6 boxes and the flying weirdo dude. Wack them all out in one spin - and get a secret life. Then you die somehow, and you won't lose the life you earned. Repeat to get 99 lives.
(supplied by: GI JinJi)
After geting all gems and relics and cristals at the first five levels you will be transported to level 26, 27, 28, 29 & 30.
(supplied by: james bricker)
On level 14 race through about half the race then when you see a alien sign, ram it. Then it will bring you to bonus level 31.
(supplied by: willyfart)
Secret Eggipus Rex level:
This can only be accessed through level 11: Dino Might! A cool secret here is when you come back with the Yellow Gem. Head through the level as normal, but let the second Pterodactyl (flying dino) pick you up, and he'll fly you over to a secret level.
(supplied by: YANKEEKAT35)
Unlock Colored Gems:
On levels where it shows a colored gem (except for deep trouble and hang em high)you can unlock the gem by beating the level until you see a platform with a skull on it without losing a life. Complete the secret path and the gem is yours.
(supplied by: Gameguy)