There are four mini-games, that you can play. They are: The Destroyer Droid level, Gungan Roundup, The Survival Challenge, and The Kaddu Race. To get the Destroyer Droid level, beat the game as Ploo Koon. To get Gungan Roundup, find all three of the Gungan Artifacts throughout the game (Jedi Mode Only--The first artifact is found in the Naboo Swamp level in a crevass in the cave. The second artifact is found on Tattoine.
At the part where you have to jump to little cliffs and destroy probe droids, there is a large island where if you walk towards the bottom part of the screen, you will come to a rough looking drop-off. However, if you walk off of the drop-off there will be an adobe house with items outside and the artifact inside.
The third item is found in the ruins level. I hope that you can find it because it's hard to describe. When you're all done jumping on the ruins, there will be an area where the tecture changes. That is a Gungan trap filled with Kreetles. After that there is a small hill with a Security Droid on it. If you walk towards the top part of the screen, while on the hill, you will come to a tree.
Walk behind the tree and there will be the artifact.) To get the Survival Challenge beat the game as Mace Windu. To get the Kaddu Race, beat the game as Adi Gallia. I hope that you can find the Gungan Artifacts. Have a kickass time!