With a name like Ninja, you can expect an unusual mouse. None of this running in mazes for food, Ninja is a mining mouse. Dig up treasure. Exchange jewels for cash. Sleep at the hotel to build up energy. Hotels cost. With whatever you have left purchase upgrades at the store. Choose wisely.
As you provide Ninja with better tools, you will be able to excavate more and get more food. When you find a bone, the next level will open up. With each level, there is more to gain and more challenges to meet.