From what I could tell, there are 10 selectable character in Puzzle Kombat that have different super moves that effect gameplay differently.
I wouldn't be surprised if there were a few hidden characters unlockable in this mode, but we'll have to wait to see.

I've seen about 2 or 3 different versions of the select screen for Puzzle Kombat.
The first one was of course, very early in development. I can't remember who exactly was on the screen, but I know that Jade was not for sure. And then I see a newer version with Jade on it.
However, we have seen Kira (both reg. and alt. costumes) in puzzle mode. I can officialy say that she was NOT on either of the select screens.
I was very curious about this myself, because I'm wondering if everyone will be in puzzle kombat or not. I'm assuming so, because it wouldn't make sense not to include everyone.
UNLESS you pick who you want on your own select screen.
Who knows? I guess we'll all find out October 4th.

I reckon everyone u can use to begin with or unlock will be playable. We've pretty much seen everyone except Rayden, Dairou, Darrius, Liu Kang and Kobra in small figure. Not sure about supers but I hope so.