[3.9] Self-Cast Ice Nova Necromancer [This build does not work anymore]

Sirus (Awakening level 8)
Plaza (T16) + Crusader
Delve (depth 277)
Uber Elder
Elder

Sirus (Awakening level 8, endgame gear)
Because evasion is useless in this fight, I used zealotry instead of grace. With this change, I achieved 20M Shaper DPS. I can further increase the DPS by using more offensive flasks.
PoB (see notes for the calculation of DPS): https://pastebin.com/f4AYbFVh


If you want to add your videos to the guide, please send a massage to me with a link to them and brief descriptions (name of the map, tier, etc.)

Videos from other players
HOGM(T16)

Ice nova + frostbolt.

This build uses ice nova and frostbolt as main skills. When you cast ice nova while frostbolt is nearby, ice nova is cast on top of frostbolt. More importantly, ice nova produces two explosions if multiple frostbolt projectiles are neaby, doubling your DPS.

Pledge of Hands.

Spell gems socketed in this staff are supported by greater spell echo. It makes the spells to repeat two additional times. We use spell echo support as well to make ice nova to repeat three times.
Importantly, when ice nova is cast on frostbolt, the spell repeats three times but the cast animation does not, effectively increasing your cast speed by 300%.

With these interesting interactions combined, you get 700% more DPS for (almost) free. This is why we get millions of DPS with little invest in damage.

Scold's bridle + CWDT + frostbolt.

One problem of the ice nova + frostbolt combination is that you have to cast frostbolt before ice nova, and this can be tedious. To address this issue, this build uses Scold's bridle and Cast when damage taken support. When you cast ice nova, you take damage from Scold's bridle and trigger frostbolt automatically. This setup makes this build very smooth to play.

Spirit Offering + CWDT.

Of course, we need a recovery mechanics to counter the self-damage. We use spirit offering for this purpose. Spirit offering is triggered every cast or every two casts of ice nova, which is more than enough to counter the self-damage. For my character, spirit offering recovers 1858 ES, and each cast of ice nova deals 532 damage. Therefore, spirit offering not only counters the self-damage but also recovers a good amount of ES.

Acendancy.

Mistress of sacrifice is essential because you need the spirit offering effect on you. Because spirit offering consumes a lot of corpses, Copse pact gives you up to 140% increased cast speed, which is very good for 1 ascendancy node. The shock effect also increases your DPS by 10-15%. Essence glutton gives you mana and mana regen, which are needed to support the absurd amount of mana we spend.

Level 1 cast when damage taken (CWDT) requires you to take 528 damage to trigger supported spells. If you get too mucn physical damage reduction, you will not be able to trigger spells every time you cast ice nova. Therefore, avoid getting armour and physical damage reduction unless you know the math. This includes armour from flasks and physical damage reduction from Pantheon. Also, Don't use guard skills because they reduce the damage you take.
Some shrine effects give you physical damage reduction. If you take those shrine effect "by mistake", right click the buff icons on the top left of the screen to cancel them.

You cannot run elemental reflect and no regen maps. In addition, "immune to elemental ailments" is dangerous, so reroll this mod whenever possible.

Budget gear is given at the bottom of this section
My current gear


Pledge of Hands and Scold's Bridle are essential items. The Pandemonius is not an essential item, so you can use a rare amulet instead.
For rings, unset rings are recommended for both slots. I could not find good unset rings, so decided to use one two-stone ring.

Minimum Requirement:
Mana sustain.

elemental resists until capped.

Very good mods to look for:
-Increased effect of offerings on body armour (hunter mod)
-crafted mod "gain 10% of maximum life as extra maximum energy shield" on body armour
-cold damage leech from helmet implicit
-life gained on hit by spells from rings
-reduced mana cost of skills from rings and jewels. However, make sure your mana cost of ice nova is 132 or higher, otherwise you cannot trigger CWDT every time you cast ice nova.
-Chaos resists are not required but should be eventually capped.
The best offensive mod in body chest is probably the "10% chance to gain a frenzy charge on hit", not the spell crit mod.

Because you gain ES based on your maximum life, always prioritize life over ES.

For rare jewels, look for life, ES and crit multi. Corrupted blood immunity is essential, so make sure you get it from jewels.

Well-rolled Lethal Pride is a great option because the double damage mod makes it easy for you to freeze tougher enemies.

For life flasks, forbidden taste is recommended if your chaos resist is capped. Before you cap it, use a standard life flask like this.


Unique items that are worth considering

The gloves give you +2% chance to crit, which is very strong. Because we use 800 mana in less than one second, we can keep the buff effect. The only downside of these gloves is the lack of resists.

These boots give you ES on hit, resists, ES and evasion rating. The downside is the lack of life.

Budget option:
All you need is Pledge of Hands and Scold's of Bridle. Both of them are cheap at the time of writing. 6-link on the staff is ideal but not necessary. If you use 5-link, use unique gloves "Voidbringer" as well to increase the mana cost of ice nova.
It is important to trigger CWDT every time you cast ice nova, so your mana cost should be 132 or higher. You can use a 5-link body armour. In that case, drop culling strike support.
For other pieces, use standard rare items with life, ES and elemental resistances.
An amulet with the cold damage leech mod (incursion mod) is recommend as a budget option.

6-link setup
(vaal) ice nova
spell echo
arcane surge
intensify
hypothermia
cold penetration

Level 5 awakened added cold damage support is better than hypothermia or cold penetration support against endgame bosses (50% cold resist), but cold pen support is better against synthesis or delve bosses with the elemental resist mod.

cast when damage taken (level1)
frostbolt (level 11 or lower)
greater multiple projectiles
(awakened) curse on hit
frostbite
culling strike or slower projectiles (level 1)

Use of slower projectiles makes sure that all the explosion hits the same target, at the cost of clear speed. With culling strike support clear speed is better, but you will most likely miss the last two explosions while bossing, losing 33% of your DPS. I prefer slower projectiles support. Don't level up slower projectiles because doing so will reduce the projectile speed of frostbolt too much.

4-link setup
cast when damage taken (level 1)
frost bomb (level 10)
desecrate (level 7 or lower)
spell cascade

cast when damage taken (level 1)
arctic breath (level 8)
bonechill
power charge on critical

Other gem slots
cast when damage taken (level1) - spirit offering (level 8) - (purifying flame or volatile dead)
flame dash
clarity
vaal grace

Use purifying flame, volatile dead, or vaal RF if you use two unset rings. purifying flame creates consecrated ground, which increases your crit chance by 100%. Volatile dead consumes three corpse per cast and increases your cast speed. I found that my PC couldn't handle the increase in cast speed, so I decided not to consume more corpses.

Buy a 21/0 (vaal) ice nova gem when you hit level 72. It's very cheap. Also, make sure you check the prices of both ice nova and vaal ice nova. For some reasons, vaal ice nova is often cheaper than ice nova. From my experience, vaal ice nova is pretty weak for this build, so use ice nova if vaal ice nova is more expensive.

Our aura setup is grace-clarity-aspect of the spider. You can replace grace with an offensive aura, like Zealotry. However, I found my dps to be more than enough, so I decided to look for more defense.

PoB: https://pastebin.com/42d4d1Ex
Ascendancy Points

Commander of Darkness is recommended as the first node because other nodes are useless while leveling. Respec it when you complete the final lab.

level 72

level 89

level 96

Bandits: Help Alira.
Pantheon: Soul of the brine king, Soul of Shakari
Don't take physical damage reduction from Pantheon! It reduces the self-damage and destroys the concept of this build!

skill gems

passive tree

Gear

CoC ball lightning

Q. The self-damage is too high after casting ice nova several times. I cannot sustain my ES.
A. Spells supported by CWDT has a cooldown of 250 ms, so you can cast roughly 4 times per second at most. If the cast rate of ice nova exceed this limit (which you do) , you can no longer trigger spirit offering every cast of ice nova. You can see in my videos or the gif at the top of the guide that my ES is dancing. This sucks, but there are no ways to avoid it. The solution is to gain more ES from spirit offering to counter the self-damage. The ES gain from spirit offering is proportional to (base life) * (increased life + increased ES) * (effectiveness of offering). This is why i recommend to get as much life as possible. The increased effect of offering mod helps as well.

Q. How about Leash of Oblation, a unique belt that allows you to use all three offerings?
A. It reduces the effectiveness of spirit offering, which is too much a downside. Also, you have to invest too many gem slots to use all the offering.

Q. My DPS sucks. Why?
A. Buy a level 21 (vaal) ive nova gem. Make sure that you trigger frostbolt every time you cast ice nova (at low cast speed). To check this, go to your hideout and cast ice nova once. If frostbolt is not triggered, something is wrong (mana cost, armour, fortify, etc). Also make sure you use the recommended flasks. Diamond flask is especially important.

Q. What is the best amulet anointment?
I like what I'm using now. + evade chance is nice, the elemental resists helps a lot to cap chaos resist. Other choices are: Crusader for damage, Constitution for life, and Whisper of doom for +1 curse.