How to finish Giana Sisters DS
How I did it: The game isn't hard by any stretch of the imagination, though worlds 7 & 8 get a bit more interesting.
Just kept playing a few levels here and there when I had a few minutes to waste, and I was soon finished!
This is a bit of a tangent, but there's only one 'sister'. You are
Giana, and your upgrade turns you into the punk version of Giana, not
someone else. There also isn't a two player mode, so no 'sister' there
Lessons & tips: There's really nothing to this game, just keep playing it and you'll eventually finish it.
Resources: If you need help with any of the trickier red crystals, there's youtube walkthroughs available.