9999 experience and 9999 gold
Before battling Jade in Obelisk, he will ask you if you want to join him. Answer "Yes", and whenever he asks you if you want to change your mind, answer "No". Do not push any buttons and he will soon say, "I'm bored. Entertain me!". After this, there will be a battle scene. You will fight a D.Flea, a Crab, a Flower, a G.Slime, and finally an M.Slime which, when defeated, will give you 9999 experience and 9999 gold.

Getting the Emperor sword
Check by the throne after defeating Jade to discover the Emperor Sword. Search the right hand pillar in the same room for the Star Hammer. Use this in combat to produce the Comet spell effect.

Getting the Tri-rang
The Tri-Rang can be found behind Pagoda after Nina learns how to fly, and before Pagoda has been activated. Search directly behind the twin towers of Pagoda to find it.

Getting the Rod5
With the Sphere, you can also reach Tunlan. Fall down a pit to the left of the vault in the princess's house, then search the box to find the Rod5. This is used to fish at the wells.

Finding C.Fish
Go to the third Dragon Shrine and go west to a piece of land sticking out into the lake. Fish on the very end of it to catch a C.Fish.

Chun Li cameo
When you visit Bleak, go to the boy who thinks he is a magician. He will say "Put a hundred coins on the table and I will make them disappear". Agree to his request and wait for him to say "Look behind you." Say "No" twice, then say "Yes". You should see Chun Li practicing her lightning kick.