I downloaded the graphics pack and found several sprites with one key background color.
In the documentation is a quite annoying procedure by creating sprite sheets then replacing the color which still leaves us with a lot of space wasted.

I added a new feature to TexturePacker to make this much simpler: It detects the background color and replaces them with transparency. See a small example here.

No extra magic needed – and the sprite sheets will be prefectly optimized!

I used the new version of TexturePacker and it supports aliasing. So that means that the butterfly is even more compact than before because it detects sprite images that are the same (say one frame of flying and sitting use the image). Zwoptex is adding this feature to the next version. But I think the heuristic mask (which enables removing a background colour) is unique to TexturePacker.