Will Krystal be a playable character super smash bros brawl?

Unfortunately, no.

From the Star Fox series, Wolf is the only addition to the group in Brawl, Fox and Falco stay in.

I'm told there are some characters that can be unlocked through a series of cheats...however, I have yet to confirm this, and know not who these "hidden characters" are, or whether they work or not.