The Behemoth aren't fools, they understand that adding ninjas not only adds awesomeness, it compounds it. (Seriously, try it out. Take any noun, say "plus ninjas," and tell me if it's not awesome. Christmas. Oregon Trail. My cousins' confirmation. Told you.) So word's out via the official blog that you can count on Ninja as another character, and Skeleton as still another.
Ninja carries a sai and a coffee mug, described in a pureley def4. That has to be an inside office joke. The mug is purely defensive. There's also a haze/halo around Ninja in the screens provided by The Behemoth, so does that include invisibility, camouflage or teleporting, or is that just a motion effect? Dunno.
Second character just announced: Skelly, whose weapons seem to include a sword and a bow-and-bone arrow. Plus from gameplay screens, he's either blocking or projecting some kind of energy attack.
Full screens after the jump.
Castle Crashers: Ninja and Skelly [Castle Crashers Development Blog of Love, via Xbox 360 Fanboy]