I've already finished the game (Transformers-Autobots) and unlocked all of the Autobots except for Warpath & Silverbolt, any tips on how do I unlock them?
I think Silverbolt can only be obtained through a code which is listed in the Cheats section above if you're using GameFAQs. For your convenience, the code is 10141. As for the other character, the reason you're missing it is because it is a golden disc you are missing, re-enter a stage you don't have 100% in and you'll find it soon enough. You can pause the game and it'll tell you if there is a missing Bot in the stage.
For Warpath go to the second last story mission called "Destroying Trypticon Space Station". You will need an air bot. At first your in a room. Instead of moving forward turn around and go to the window. You should notice a disk, that is warpath. TO actually get there leave the room to the open platform where you first fight. Transform into a jet and fly into the space and navigate your way on the outside of the room you came from to get warpath
Plus don't forget you can unlock Ramjet via code too. The code is within this board.
Also have you unlocked all the available Decepticons too? You can unlock 11 just by this game alone.
Nintendo translates as Leave luck to Heaven.