So far, i've seen :
The Outlander. He pushes the target (enemy or ally) 1 or 2 tiles away. Does not deal direct damage. If the Outlander kicks a target into another one, they are both stunned for next turn.
The Slaver. He pulls the target (enemy or ally) from 3 tiles away to the tile right in front of him. Does not deal direct damage. If the Slaver pulls a target into another one, they are both stunned for next turn.
The Guardian. She have a shield able to negate almost all damage from melee as well as arrow. It's passive, as long as she is facing the hit. She can also use her active skill to Stun the target for the next turn. Does not deal direct damage.
The Cyclop, it seems we don't actually play it more than one mission ? Can deal direct damage, to kill its target.
What else ?
An archer ? able to deal damage from distance.
A mage ? able to change its place with anyone, or maybe at higher level to switch two targets position. Could open a lot of puzzle or fun situations. Could also be able to leech-healing, taking 1 life to anyone, to give it to anyone.
A psycho ? able to take control over an enemy, but get hurt doing so. So, each new controlled target = one less hitpoint.
A flyer ? able to pass over traps and water, and carry one target in its claws
Also, if i'd like to see more characters, i'd prefer i think to have more than one skill per character.