How do you unlock the ninja bike in race?

1. Complete all the levels in the game. This means beating all the levels in all the different game modes, including "Campaign", "Time Trials", and "Challenges".

2. Collect all the hidden coins. There are a total of 100 hidden coins scattered throughout the game. You can find these coins by exploring the levels and looking for hidden areas.

3. Once you have collected all 100 coins, you will unlock the Ninja Bike. You can then select it from the "Vehicles" menu in the game.

The Ninja Bike is a very powerful vehicle that can help you beat the levels more easily. It has a high top speed and good handling, making it perfect for racing around the tracks.