Possibly the funnest build I've ever played: Selfcast Ice Spear/Arc Archmage Ascendant

This is not the strongest build I've ever played, although it's honestly pretty decent for a total hipster build. If you're looking for a build that never dies and can obliterate A8 Sirus in seconds, this is not that. But if you're looking for a build that can do hard content without trivializing it, so that it still feels like an actual challenge, I recommend checking it out.

https://pastebin.com/PPnt1SzS

Basically, this is a selfcast build using Unleash with Arc for clear and Ice Spear for single target. 10k ehp, Arc will blow up the entire screen and then some in one cast as long as you crit, and Ice Spear does about 6.5M damage per cast under ideal circumstances. Ice Spear can definitely be a little tricky to aim, but I find that it's super satisfying when you land a direct hit and see a significant chunk of a boss's life vanish. I've probably got about 30ex worth of gear at this point, quite a bit of it found or crafted myself, but you can get it running for <10ex.

Elder Kill