I think an ability that could add an interesting dynamic to the game would be Defeat, but it punishes the player who was defeated. For example, you add a powerful card (8 and 5, 3 stars) to a powerful clan such as Junkz. You then give the card the ability Defeat: -3 pillz, min 2. So if you lose with that card, you also lose 3 pillz. I think this could make for some interesting play.
No, not good. Would be a perfect cheap finisher that can go all-in once the opponent is softened. Without any risk. And the opponent might in fact have to win every other round so to not allow the all-in of the overpowered card. Too many situations where the disadvantage becomes null.