How do I get the Crystal Heart in Chapter 4?

In one area during the second part of Chapter 4, the Crystal Heart is positioned high above Madeline and apparently out of reach:

The area contains a Mario-style block at the bottom, but I'm not sure how this relates to the puzzle. Any ideas?

Solution 1:

I tried holding ↓ on the D-pad in different places, assuming that the Mario reference was related to some sort of hidden "pipe", and it turns out I needed to stand on top of the white Mario block and hold down:

The tricky part is that you need to hold ↓ for longer than you might expect, until Madeline "sinks in" and goes into the background. From there, you can use the background terrain (the light pink area) to reach the Crystal Heart.