I had the same issue, and could never get a cast off. What worked for me was using my mage, popping a noodle cart, and waiting until he is almost right over me. Then, jumping out of my cart, mounting up, flying straight up to where he would be, and popping my arcane burst spell. What you may not realize, is that even though you can't see him, you can still hit him with aoe attacks. It takes practice, and luck, but eventually you can judge it right, and nail him. You will know it worked because you will go into combat, and your combat log will show the target trying to hit you. Then, just use a few more aoe spells, and he will die. Finally, pop a noodle cart where the body should be, and presto you can see the shiny corpse. Good luck!