Explanatory Notes on Vorpal Hurricane

Where Vorpal Hurricane talks about the start and end of your opponents' "actions", it means the start and end of their turns.

Example: You're fighting three opponents. You start a Vorpal Hurricane with your greatsword while one of them (A) is next to you, and the other two (B & C) are two squares away.

A goes first. As soon as his turn comes up, you get an attack on him, as he is adjacent to you. You resolve this attack before he resolves any of this own actions.

B goes next. He takes a 5 ft step to flank you with A, and makes a full attack. At the end of his turn, he's still adjacent to you, so you get an attack on him. This attack is resolved after all of his actions have been resolved.

C goes next. He's got Mobility 3, so he steps forward, hits you once, and backs off 10 ft. Since he neither started or ended his action next to you or in square you threatened, you don't get an attack on him.

Finally, don't forget that Vorpal Hurricane works on any square adjacent to you, as well as on any square you threaten. Just in case there is ever a square next to you that you don't threaten for some reason, or a square you threaten that isn't adjacent to you (such as with the Tall trait).

Vorpal Hurrican 9

If you have the highest level of Vorpal Hurricane, you can activate the ability as a free action at any time during your turn, and carry on doing other things afterward (just like in the middle mastery, where it says that you can move before or after activating the ability).

Remember that an opponent only triggers an attack from Vorpal Hurricane if they begin or end their turn in your threatened area. So you don't get to make Vorpal Hurricane attacks on everyone you move apst during your own turn.

Vorpal Hurricane and Attacks of Opportunity

Vorpal Hurricane is considered to be an attack action and does not provoke Attacks of Opportunity.