The G4 Twilight Sparkle combines an existing 3" body with new face and mane design (with bangs!), while the G1-based Twilight has a brand new pearlized design with the looks of the original pony from the 1980's.
Both come in a combined see-through package showing a design of Twilight on one side and Twilight Sparkle on the other side. Each side also shows the My Little Pony design from their respected era. The set will be available for $19.99 and debut at the San Diego Comic Con. Afterwards the figure will be available on the Hasbro Pulse website while stock lasts.