At any moment, as long as I concentrated on it, I could sink into the floor as a black silhouette. As a shadow, I would slide along the floor, under people and objects as if they weren't there.
I was at someone's house, and she asked me to teach her how to do it too. I explained that I could, but it would be difficult. I had been taught by someone who got the ability as a class skill, but my own class didn't get it (I don't know why this part was so video gamey. Maybe it's because I've been reading so many isekai). This meant that, while I could teach her, it would be harder for me to to teach the fundamentals needed to understand it first.
I had to teach through demonstration, using the ability and having her observe all the different aspects of it one at a time. First I had her kneel on the ground above me while I was in shadow form and [HORNY DATA EXPUNGED].
Then I showed her how, despite how the shadow followed the contours of a surface, they didn't actually bend. I slid along a flat and level floor, until reaching a ramp. In my shadow form, I could still feel my body. I was aware of the world around me, but only saw myself in darkness. I started to go down the ramp head first, and my head didn't lower. It was as if something held me perfectly level, as I felt the empty space under my head. But the shadow still bent as you would expect them to.
The next demonstration was about the moment of the transformation. I concentrated, and felt my body fall down through the floor. But at the same time, the ground rose up around me where I lay. Both of these were true.
After this, the dream gets fuzzy