These are the tsum tsums I think should really be in the game, and what I imagine them to be. Also check out Character Strategy and check if you have a Tsum Problem. 

Star Wars 

Seriously, Disney owns Star Wars now, so where are the Star Wars Tsums? I mean they're doing Star Wars merchandising on pretty much everything else!

Darth Vadar

Darth Vadar's skill should be that he uses the force to shake the screen and kills all other Star Wars Tsum. If there are no other Star Wars Tsums, then he will pick one type and destroy all of that one. 

JABBA THE HUTT

Jabba's skill should be a trapdoor opens at the bottom of the screen and a bunch of Tsums fall through the bottom.  

Jar Jar Binks

Jar Jar's skill is jump around and shoot the screen, missing most of the Tsums and collecting a few. I know this sucks, but so does Jar Jar, so it makes perfect sense.  

Yoda

Yoda appears on the screen and bounces all around with two lightsabers, destroying the Tsums on the screen. It should be a Pete/Beast level skill. 

BB-8

His skill is to swirl around the screen in a U shape (like the opposite of Hawaiian Stitch). 

101 Dalmations

Cruella De Vil

Cruella's skill grabs all canine Tsums on the screen and drops them up top (like Alien). If there aren't any canine Tsums, she will take any black and white Tsums instead (Baymax, Oswald, etc.)

Pongo

Pongo is the daddy dog of 101 Dalmatians. When his skill activates, 101 puppies rush the screen taking out a large amount of random Tsums.