Level 12 is the twelve level of the Main Tunnel in Run 3.
This level should not be too difficult. If you are using the Skater, make sure that when you jump, don't fall into holes. If you want to jump farther, you need to gain more momentum by staying on the ground. Jumping more doesn't equal to jumping farther. But please be aware that there are quite a number of crumbling tiles, so pay attention to the ground in front of you.