If you stand behind W4-H4 when you first meet her then press z or c you can grab her bum.
edit OK it's a bit too easy. I think my old Sega CD version of columns was harder. But good for casual. However maybe the adventure mode should be more than just rooms to explore. Basically, this is like a demo version. Keep working on it and put some work into the non-puzzle areas with some puzzle platforming to get secrets, like not necessary anything.
OK found a bug. I was holding a stack when the roof came down and after that new pieces hung in the air and I couldn't pick anything up. Then when I died I was at the bottom of the pile with the holding item animation perpetually on.