The first time I faced Odin I hadn't "optimized" my display, so I couldn't see him. He kept popping in and out so by the end I got bronze.
The second and third time I faced him none of my attacks registered. I was hitting him from the start to the end of the battle, not one DoT landed, not one skill that gives me a buff actually triggered. I watched my skills report damage but none of them appeared to affect his HP and by the end I scored Bronze again. It's hard enough to find a target you can hit without it vanishing even with all effects turned off, but couple that with the fact when you CAN see the target none of your attacks count and the whole event becomes pointless unless he spawns on top of you and you're first to hit him.