How about traps ? perhaps spell or ability

[Warmage]

Just thinking later it might be cool to have some sort of traps that you can lay.

[Kvothe]

Traps rule.

[Ross Przybylski]

Hmm...perhaps we need a Thief or Engineer character, eh?  Definitely doable.

[Joshua]

I like the idea of adding another character: "Engineer" (in most games, that's the name of the character who lays mines etc)

"Theft" could be character that can steal cards (card cost = 1). One of his other ability could be "Stealth" which can be useable anytime (makes him invisible) for one turn, and have a cool down of 2 turns after its use.
"Healer" = low str and low hp and can heal a target
"Tanker" = high def and health, but very low strength.  Hrmm... what ability could he have?