Benefit: When you hit an enemy with a power that dazes the target while you are using a mace, the target also takes a penalty to attack rolls equal to your Constitution modifier for as long as it remains dazed by your attack.
Obviously this works with weapon attacks with a mace, or with implement attacks if you have a way to do it (Ironscar Rod, Unforgettable Cudgel, or Crusader's Weapon for example).
However, what does "use" mean here? If, for example, you are wielding a mace, and hit an enemy with a power that dazes that doesn't have the weapon/implement keyword, are you "using" it? Does "using" require you to be "using" it on that attack?
You hit an enemy with Dragonfear, which does not have a weapon or implement keyword. You are holding a mace. You also have the following feat:
Dragon's Terror. Benefit: One creature you hit with dragonfear is also dazed until the end of your next turn.
Are they Dazed and -2 to hit (from Dragonfear)? Or Dazed, -2 to hit from Dragonfear, and -CON to hit from Dizzying Mace?