A card can be a (somewhat) useful means of distracting your opponent in combat, but as a weapon...
Well...
Paper-cut. That's as good as you're gonna get with one of those.
A blade card? That's not a card. That's just a rectangular throwing blade with a playing card imprint on it.
Unless you can channel some energy into the cards like Gambit can...
![](http://www.freewebs.com/th8bitgod/gambit1hk1.jpg)
I'm surprised the cards don't burn up or vaporize. I wonder what they're made of? Hmm...
Put another way, cards areas useful as a range weapon as a Bat'Leth is as a melee weapon.