Making different card effects.

Think of it like this, every card should have it's base properties and then has an Effect property that you extend to be all your effects, here is an example.

 public class Card
 {
    public string Name;
    public int ID;
    public Effect effect;
 }

Then your Effect class

 public class Effect
 {
    public virtual void DoEffect(){}
 }

Then your damage effect

 public class DamageEffect : Effect
 {
    public int Damage;
    public bool AreaEffect;
    public override void DoEffect()
    {
        if (AreaEffect)
        {
            //damage all
        }
    }
 }