Sadly, as was posted in another thread, the ARR developers use a "true RNG" algorithm to determine what loot drops.

Of all the times that I've seen Scylla's Coat of Casting, it has dropped once... and I didn't win the roll. (I rolled a freaking 4.) Sure, there's better chest pieces out there, but if I want to be able to do second coil (after I've unlocked it, of course) then I need something better than what I have now. I refuse to get the Evenstar Coat because I hate the "tail condom".