It’s really difficult. I don’t know how well I can explain it: When you are touching the ground, click the door and then run as usual. When you go to enter the room, wait about half a second or a little less then click the door again. But don’t click too fast or you’ll level skip resulting in death since the next level’s spawn is vertical. If you aren’t running Cat Ninja full speed, or just want to know exactly when to click the door for the second time, you should click just as the blue thing in the bottom right starts to appear.