An example of what I am trying to understand is the power Brash Assault. The effect states "Effect: The target can make a melee basic attack against you as a free action and has combat advantage for the attack. If the target makes this attack, an ally of your choice within 5 squares of the target can make a basic attack against the target as a free action and has combat advantage for the attack.
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My GM says that I need to hit with the attack to offer the effect and gain the ally attacks. I think he is wrong and the effect happens whether I hit or miss. Please advise.