Witch
OccultistThe Vaal Ice Nova of Frostbolts Occultist can do all content and do it well, using 
Vaal Ice Nova for clear and Ice Nova of Frostbolts primarily for single-target DPS. These are conveniently combined into a single skill gem.
See this guide for the leaguestart version: https://mobalytics.gg/poe/profile/camaronincheese-fs849b/builds/3-29-vaal-ice-nova-of-frostbolts-occultist-leaguestarter
Notes for all budgets:
If you're doing an easier farm and just want mega AOE and clear, swap out 
Inspiration Support for 
Vaal Temptation Support and swap out 
Badge of the Brotherhood for 
Ashes of the Stars. You should easily be able to tank the damage from Vaal Temptation Support, so long as you have a recover ES on hit Watcher's Eye and an ES pool of 5000+.
You can also reduce the DoT further by taking the Arakaali and Ralakesh pantheons, and 
Lethe Shade on the passive tree if it's still too much for you.
Getting %phys reduction is also good for tanking the damage. You can get that on your chest, from endurance charges, and from a watcher's eye pretty easily. Though the ES recovery on hit watcher's eye is way better in my opinion, since you'll actively recover as the nova is cascading.
This results in the giant AOE cascades that you see in my video. You'll notice that the AOE for the boss showcases is smaller, and that's because I focus more on the DPS than clear for those guys.
Important things to keep in mind for the build:
Your mana regen needs to be 2x your mana cost per second if you're using spell echo. And it needs to be 3x your mana cost per second if you're using greater spell echo.
This is because the echoes take place on your frostbolts and not from you, which is how we get so many hits and so much damage with this build. You're actually casting twice as fast as you normally would with normal spell echo, and three times as fast with greater spell echo, because the locked casting animation you normally get with spell echo doesn't happen with this skill.
These aren't repeats, so things like the caster mastery where the final repeat has increased AOE doesn't work. it's an expand instead, technically speaking.
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You want to run as low of a level clarity as possible to fit everything in at the high end without needing to spend passive points on mana. You have some options here.
Mana isn't a dead stat for us. Higher mana means we can run a higher level clarity. Also means higher base mana regen.
Mana regen tattoos are helpful if you can't get mana regen in other places
We do have another wheel for mana reservation efficiency by the staff mastery in the top left of the passive tree we can take if needed, but you'll need to sacrifice passive points for it
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The skill DPS estimation listed in Mobalytics is for a single ice nova. So multiply that by 4 for 
Spell Echo Support, or by 6 for Greater Spell Echo Support
MAP MODS TO AVOID:
These are technically doable. But annoying and we don't want them.
1. Cannot regenerate life or mana. You can take a mana flask into the map if you HAVE to run the map. But it's bad.
2. Monsters steal charges. Can be done, since you generate power charges extremely quickly. But still quite annoying
3. Less armour and block. Again, can be done. But makes you much less tanky. Why is there no "less evasion" map mod?
4. Reduced max resistances. If you're scaling map effect a ton, this can reduce your resistances by an insane amount. Which again, can be done. But you risk dying a lot more easily.
