I had the following skills loaded:
-Capture Signet
-Capture Signet
-Capture Signet
- Useless Beast Skill
- Useless Beast Skill
- Throw Dirt
- Point Blank Shot
- Whirling Defense
First, for some reason the mirror doesnt want to use his bow, so he rushes you instead of sitting back and plucking away. So when you first get in, put up whirling defenses while you attack him with Point Blank Shot (Shortest Refresh Time I could Find with 3 for a +dam shot). Once Whirling Defenses goes down, u put throw dirt on them. This gives you approximately 20+ seconds until he can effectively strike you. Giving you a bit of a lead. Now he will probably use throw dirt and whirling defenses against you in the beginning (he did to me) but stick with it, theres a large refresh time on it, so he wont use it again basically. Just dominate him for as much of those 20 seconds you can, and then when whirling defenses come up again, use it again (I used it with 100 hlth left and he had less than 50). Easy...
So, basically
Fight Starts
Use Whirling Defenses (16 Secs with 9 Expertise)
Use Throw Dirt (11 Secs with 9 Expertise)
Keep using point blank shot the whole fight when it becomes avaliable
Use Whirling Defenses when it refreshes.
Dead Mirror
That's all... easy as hell when done right. Good Luck.