It's been a while since IW mesmers had any degree of popularity in RA. But I have to say, theyre not as bad as one might think. With Illusion of Pain on top of Illusionary Weaponry you can put out decent pressure damage bypassing most defences and armor.
That said, I still havent been able to come up with a build that I can actually call a good one. At best it's "Good for a IW mesmer but sucks comparing to literally anything else."
Shadow sin skills honest you can put damage on a target but your weakness is no defense. Since you do not hit anything there are a few skills that will shine. Speed increase and taking 1/2 damage is allways nice. Also there is one for increase armor and Health regeneration.