An actually good build for that would be a sorc, but I think sorcs suck, so I would go druid 20 in fissure, 20 in firestorm(for synergies), 5 in carrion vine, 5 in dire wolf, 5 in oak sage, and a total of one in each of the prereqs adding to a total of 5. that way, you hide behind minions and fissure-nuke anything that gets past them so you never use any durability on your ethereal stuff. You could also go fishymancer, but I would want as many opportunities to massacre things with fissure as possible. I don't know if any of that's your style, that's just how I'd go about it.