A ceiling that the player will stick to when going upwards and holding a Jump button.
Enemies will also stick to the ceiling as long as they have upwards vertical speed. Sprites in "Stunned" or "Thrown" state will stick to the ceiling until they either move away from it, or the player grabs it.
When going downwards, the player and any sprite will just fall through.
This is a very interesting idea, however, I felt the submission was lacking a bit. I also think that sprites shouldn't 'jump' when reaching the end of these blocks, perhaps by zeroing (?) the Y speed. By the way, next time, do NOT forget to set up the tags or your submission may be removed. Good work, still!