D
Now maybe I'm just dumb, But I was a lvl 18 R/E and I could not beat the Dopleganger. A few minutes ago I was playing and I thought of something, the Dopleganger doesn't have a pet! So I put all points in beast mastery and extra points in marksmenship, and equipted all beast skills (filled extra places with Capture) and fought him. Sure enough I won the first time in. Just thought I'd let all you rangers know.

I think he might've been interrupted.