D-pad

Hit up on the D-pad, and the background music will change as the background itself becomes the Demon King's castle....

Source: tatoeba (328148)

The strategy that has dominated recently for the last couple of years is to tap the d-pad as fast as humanly possible with one finger, known as hypertapping in the gaming community. In NES Tetris, this skill is crucial, since the speed increases when moving up levels, culminating in level 29, where the pieces usually drop to the bottom of the board in less than ⅓ of a second. However, hypertapping has several limitations.

Source: wiktionary

Like the name implies, a hypertapping player simply presses left or right on the NES d-pad their desired number of times.

Source: wiktionary

The first known way past the brick wall of Level 29 was a technique that became known as hypertapping. By using a special grip that lets you vibrate a finger over the D-pad directions at least 10 times a second, you can effectively skip the "delayed autoshift" (DAS) that limits how fast pieces can move laterally when the D-pad is held down.

Source: wiktionary