When an enemy uses a power that grants multiple attacks, does that give the fighter an attack against the enemy?
The problem is that there are at least four possible definitions of 'attack', and for three of them, the Ranger's Twin Strike doesn't involve an attack that does not include the Fighter.
1. A power with the Area keyword is an "Area Attack", whether it's an attack power or a utility power. So Twin Strike is either a Melee Attack or a Ranged Attack, and in either case, it includes the fighter as a target. Wall of Fog, a utility power, is an Area Attack, but since it has no targets, it cannot include the fighter as a target - Wall of Fog would trigger the fighter's attack.
2. Twin Strike is an Attack Power. If we assume that this is what is meant by "an attack", Twin Strike includes the fighter as a target. Wall of Fire is an Attack Power, but since it has not targets, it cannot include the fighter as a target - Wall of Fire would trigger the fighter's attack.
3. Twin Strike is a power that contains a line headed "Attack". If this is what is meant by "an attack", then Twin Strike's Attack line includes the fighter as a target. Wall of Fire has no Attack line, so it is not an attack, and would not trigger the fighter's attack.
4. Twin Strike explicitly states that the character makes two attacks. One of these includes the fighter as a target (and does not trigger the fighter's attack), but the other does not include the fighter as a target (and triggers the fighter's attack).
Unfortunately, it's not made clear exactly which definition of 'attack' is being used in the phrase "an attack which does not include the fighter as a target".
-Hyp.