From when I fought Rooke, I just remember me and Subodai charging towards him like maniacs. But I did the battle with my friend yesterday. If you're a swashbuckler, great! If you're not, bring a swashbuckler friend who can turn you and your companions all invisible, then sneak up on him and use your strongest attacks. Hope this helped!
I put bonnie a square away from him and I used some how damaging companion to go between bonnie and rookie so he couldn't get knocked away I eventually defeated him