The official Star Wars site at Hasbro.com made available a PDF catalog. Speculation at TheForce.net's forum makes a bold argument that the "secret" figure masked out could be a grown-up Boba Fett.
DarthTaters posted on 3/31 to TheForce.net's Jedi Council Forums:
Found something interesting on page 14-15.
Battle Figure game.. They have a secret character..
hmmm, I wonder what this could be? Another jedi? Another dark jedi? Sifo Dyas?
Looking at the outline of the picture, it looks a lot like an adult Boba Fett..
Anyway, if anything the catalog has some great pictures.