What's the name of that Kung Fu where you can fly by stepping on your left foot and right foot?

It’s called Qinggong.

Let’s first talk about the source of the rumor. Which paragraph is it that says “the left foot steps on the right foot and flies into the sky”?

Some people say that in "Yitian", when Zhang Wuji was fighting Guangming Ding, he carried a fat monk and used the Wudang Ladder Cloud Zong Qinggong to fly several feet high with his left foot stepping on the right foot.

Then let’s take a look at the original text:

Zhang Wuji grasped Yuanyin in his left hand and held the Zen staff in his right hand. He jumped up, his feet pointed at the center of the circle, and the Zen staff in his hand could only be heard. With two hehe sounds, Yuan Xin and Yuan Ye fell to the sky at the same time. Fortunately, both monks had extraordinary attainments in martial arts and remained calm in the face of danger. The two gold-plated iron Zen rods weighing dozens of kilograms did not bounce back and hit themselves.

As everyone screamed, they saw Zhang Wuji grasping Yuanyin's tall body and turning slightly, landing lightly on the ground. Seven or eight people from the six major sects shouted out: "Ti Yun from the Wudang Sect. "Vertical"