How to get enemy boss battle chips:
Go to the park after fighting a boss. Fight the boss until you get an "S" rating, which can be obtained by beating the boss and not getting hit, only getting hit once, beating the boss quickly with a great deal of health left, etc.

The Final Boss:
When you collect all of the navi chips in the game, you will get a email from Mayl saying that there is something weird in Den Area 3. You will need a few double jump chips for this. When you reach the end of Den Area 3, use your air shoes to jump onto a ledge and keep going right until you see a gap above you. Use another double jump and you will enter a room with a security cube. It will unlock if you have all the navi chips. You will see a green teleport which will take you to the real final boss.

Action Figures:
After you beat a boss, go back into the real world. If you look carefuly at the table under the poster in Lan's room, you'll see the action figure of the boss you have just defeated. Later on it will be hard to see which is which because the table will become cluttered.

Thanks to Revolution readers Eddie Almbarak, the shiny1 and vince!