Well the main feature would be powerstrokes. If you open this with Inkscape, all the powerstrokes would be shapes with tonnes of nodes.

I also used inverse clipping. I'm not sure if Inkscape has it or not, but I think it doesn't, so the shapes I used inverse clipping on, won't be shown correctly. I also used Fill between Strokes, but I don't think that does any funky stuff if you try to open it with Inkscape. After all it's just a shape.

Ponyscape also has features like Elipse by 5 Points and Attach Path and others, which can be quite useful, but I havn't used them in this vector.