[1.3]Cold Witch guide for beginners (Lvl 1 to Atziri)

You can either have a life based build or take Chaos Innoculation.
Even if you plan for CI it is recommended to start as a life char. Why? It is much easier to get life on gear and to have a big life + ES pool than to level with only a much smaller ES-only pool. You will get passive respec points along the way that you can use to spec out of the life nodes later.
The usual progression is: You go life until you reach act 2 merciless (you should be in your late 50s lvl by then); some even delay going CI until they defeated merciless Vaal. At the beginning of act2 merciless you will have 14 passive skill refund points you can use to spec out of life. By then you should have collected ES gear that will get you 2000+ ES (another reason CI is a bit tricky if it is your first char).


Your first steps should be to get life nodes and lay the basic path for the final build :

The following setups are for 5 links. I put the least important support in last place, so if you only have a 4 link just drop the last support gem in the different setups.

Freezing Pulse – Lesser Multiple Projectiles – Faster Projectiles – Life Leech – Spell echo - (Cold Penetration/Faster Casting/Inreased Critical Strikes)

Lesser Multiple Projectiles. A must have for FP as the projectiles can overlap and multihit a single target. With FP’s 100% build in pierce (the ability to travel through the enemy it hits) this makes FP one of the best crowd control spells in the game.

Faster Projectiles. A must have on a normal Freezing Pulse as its projectile dissipates while it travels, dealing less damage the further it goes. With Faster Projectiles FP will not only have a much farther reach allowing you stay in a safe distance from the mobs it also increases the damage at any given point in its traveling path compared to a slower (and quicker fading) projectile.
BTW if you don't have quality on your FP nor want (or can) use faster projectiles you could buy the unique Karui Ward amulet (should be available for 1 chaos). It gives 30% increased projectile speed.

Spell echo Added with 1.1.5 it is a must have. Free additional cast! Due to limited links it is now more important than ever to get a freezing pulse with quality so you can replace faster projectiles with it. If you haven't got quality on your FP by the time you get spell echo (library quest a3 merciless) and only have a 4L you might consider buying for 1 chaos so you can drop faster projectiles.

Cold penetration lowers the resistance of the enemy. You get a flat damage increase no matter how high its initial cold resistance. For mobs with 0% resistances that means 30+% more damage. When looking at max resist mobs, lowering the resistance from 75% to 45% will give 120% more damage, making it the best support against high resist enemies. Don’t be fooled by the tooltip dps not changing. You get more damage by lowering the defense not by upping your offense (though the final result is the same)

Faster Casting gives a nice damage boost but also increases your mana needs as you cast more often per second. (If you can’t spam your main nuke the dps increasing effect of FC is neutralized). That makes it a bit more difficult to handle than other support gems. A word of warning: don’t get fooled by tooltip dps. FC increases it, cold penetration won’t, though if you replace one gem with the other your REAL damage won’t differ that much (if at all).

Increased Critical Strikes increases crit chance. More damage and better defense because of higher freezing rates is a nice double effect.

Depending on the quality on your FP there are two setups i would recommend:
FP - LMP - life leech - echo - faster projectiles (in case you don't have a Karui Ward amulet to replace faster projectiles)
FP 15%-20% - LMP - life leech - echo - cold penetration

(The introduction of echo has the advantage that CI users now have less trouble with their socket colours as they no longer need 3 green off colours.)


Alternative prime spell:

Ice Spear – LMP - life leech - spell echo – increased critical damage/cold penetration

While Ice Spear starts as projectile with 100% pierce it changes into solid form after a fixed distance. The second form has a +600% increased critical strike chance in its second form, that’s a 49% base crit chance from the beginning. That makes Ice Spear the perfect spell who like to kill from a safe distance. The aoe is worse than the coned FP but you don't have to facetank on the other hand.
Due to the high mana cost of ice spear one would probably has to take Eldritch Battery though making it a bad choice for CI compared to FP.
I recommend levelling both FP and ice spear and switching between them to find out which spell suits your gameplay most. (On a sidenote: Atziri is easier to kill with ice spear)

Other useful spells:
Cold snap is a very good secondary spell especially in the early stages because of the high build in chance to freeze the enemy no matter if you crit or not. Even in later stages a setup with
Trap (for the MORE damage bonus) - cold snap - elemental proliferation - increased AoE
is really helpful in perma freezing even bosses.

Ice nova
Probably the best STARTING gem in the cold arsenal due to its AoE that chills the mobs, really improving survivability in the early stages while giving better dps than an unsupported Freezing Pulse against mobs. Unfortunately it doesn’t scale as well in late game as FP and forces you to stand in the middle of the mob, something you really should avoid in merciless and maps.
If this is your very first char you should start the game like that:


Vaal Gems
Vaal Discipline is a very good defensive option for CI builds as the ES recharge is not delayed by damage taken for several seconds. Nice oh shit button for tight situations.

Auras:
All auras should be linked to a reduced mana support gem. A full leveled red.mana will decrease the reserved mana to 71%. An aura that normally would reserve 60% of the mana would therefore only reduce 43% (it will get rounded up). There are several nodes in the tree that could further reduce those costs like Sovereignity. BTW additional quality on a reduced mana gem will NOT further reduce the amount of reserved mana when using auras but will only lower the mana costs of skills used (for example lower the cost of casting fireball if linked to it).
For a life based char only 2 auras are mandatory:
Purity of elements which will increase elemental resistance (its 40% reservation will get down to 29% with a lvl 20 reduced mana)
Clarity which will increase mana regeneration. It starts with 64 mana reserved and goes up to 520 mana reserved on lvl 20. So be careful when leveling that gem (better have two versions one lvl 10 and on leveled to 15+). Make sure the rest of your mana is enough to spam your main spell. Anyway with only two auras running one should be ok even with a high leveled clarity.
For a CI things get a bit more complicated. Not only will one need Clarity and Purity, but also
Discipline which gives additional ES.
Discipline is a 60% aura (43% with red.mana). That’s 72 % reserved mana without clarity. Things might get a bit tight here. That’s the reason for taking reduced mana nodes from the tree for another 8%-20% reduced mana. With a lvl 20 reduced mana that leave enough room for clarity (though probably not fully leveled; be careful here) and enough mana to spam the main spell.

BTW if you can get a purity of fire/purity of lightning try leveling it up in the second weapon slot. There are situations where it is beneficial to swap purity of elements for one element (Fire for crematorium or General Gravicius; lightning for barracks, crematorium piety or map piety for example)

Heralds
Herald of Ice
Gives additional cold damage to your spells but reserves 25% of your mana. If you can sustain it, use it! Don’t if you have to drop purity instead and no longer have max resists. Remember: dead witches don’t do damage.
Herald of Thunder
Works really nice with crit builds as the added lightning damage is enough to shock normal mobs on crit constantly triggering the lightning storm. It really shines when linked to curse on hit and a curse. With a high crit rate the mobs are constantly hit by lightning and therby cursed. Makes for a smooth gameplay as you don't have to pause for manual cursing.

Curses:
Use frostbite for offense and temporal chains (or enfeeble) for defense.
When playing in a party cursing elemental weakness instead of frost bite might be more beneficial as most of the times other players will be dealing some other elemental damage.
Assassin’s Mark
When reaching lvl70+ I would replace frostbite with Assassin’s Mark (formely known as critical Weakness): With high enough crit chance you do more damage with it if you have roughly an extra 100% increased critical damage with gear/support gems/tree passives. You also have a chance to gain power charges on kill which might be enough to use power charges without the power charge on crit gem (try it if you feel comfortable with the lower charge generation rate).

Trigger gems:
Cast on damage taken
It comes with a huge penalty (LESS damage) when used with a damage spell, that gets reduced when you level it up. On the other hand it increases the amount of damage you have to take before it gets triggered. You have two choices:
1) Keep it at level 1 and use it with enduring cry for some endurance charges that give 4% physical damage reduction per charge and a low level temporal chains or enfeeble to autocurse attackers (it might override your frostbite curse occasionally though).
2) Level it. As you can't use spells that are of higher level than the CwDT i recommend maxing it to 20. It will take 3000+ damage to trigger but that can happen pretty quick in merciless. You can either use it as a second defensive layer with molten shell and decoy totem (in case you don't want to use spell totem - summon skeletons as distraction).
Or you link it with Cold Snap + Ice Nova + Concentrated Effect for a high chance of freezing melee attackers that made it past your skeletons.
Option 1 is probably the most popular one.

Totems:
Highly recommended and a must have imho: Spell totem + summon skeletons. Feel free to add a blind gem for additional defense. The boost in survivability is HUGE. If you have 6 skeletons up the chance of getting hit goes down from 1:1 when soloing to 8:1 (6 skels, the totem and you). That is a virtual evasion rate of 87.5%. It is impossible to get that rate in endgame even with the best pure evasion gear.

Blood Rage:
A very useful spell for CI chars. Every kill grants you a frenzy charge that increases your cast speed by 5%. The chaos damage penalty won't affect CI chars (don't use that spell as life char!).

Arctic Armour
A spell that is really helpful when facing enemies that do physical/fire damage with very fast attacks but low damage per hit like the voidbearers on docks or tentacle miscreations in the lunaris temple. Unless you build for a large mana pool it can only be used while standing still on max level; while moving the mana cost is too high and it will shut down very fast. If you can spare a single socket somewhere use it in voidbearers/titty bitches territory.
To sustain a high level AA while moving one needs a big mana pool (+3000), a maxed clarity and ~100manareg. One can bypass those requirements by using light warp as movement skill as AA doesn't have a higher mana usage in that case.


Movement skills
Used by some players to get out of tight situations. Witches mostly use lightning warp – reduced duration to get away.
As a dagger user I prefer whirling blades. Has no delay and doesn’t need a support. Lvl 1 is enough.
Use it if you have the free socket(s). Otherwise don't. Auras and attacks are more important imho.
Before opening boxes socket a Smoke Mine gem (lvl1) and lay the mine a bit away from the box. Click the box and immediately trigger the mine. That way you avoid getting surrounded by monsters.

The above gives a lot of possibilities on what skills to use. For the undecided here is one possible build that i had good experience with in endgame:
Life build with Eldritch Battery; no extra power charges.

Chest: FPqual(or ice spear)-LMP-cold penetration-life leech-spell echo-(increased critical damage)

Helmet: Trap-cold snap-elemental proliferation-concentrated effect

Weapon: Lightning warp-faster casting-reduced duration
Shild: Clarity - reduced mana , arctic armour
GlovesReduced mana - herald of ice - purity of lightning - purity of fire
I run only one purity depending on the map mods/boss i am facing.
Boots Herald of thunder - reduced mana - curse on hit - assassin's mark (or elemental weakness or enfeeble depending on the map mods and the requirements of the party)

CI/Life:
As long as you are leveling you need not look for a specific armor type. Instead focus on specific mods: Look out for gear with life on it; second priority is resistances. It actually doesn't matter if you wear an armor based chest as long as you have the sockets for your gems on other gear pieces. The only restrictions you have to take into account are the stats requirement (you may not have enough STR for example to wear higher armor chests) and the socket colors for your gems.
Additional mods: Movement speed on boots. Useful offensive mods (aside from increased spell damage) would be faster projectiles (on the weapon). I wouldn't look for faster casting as this mod is pretty expensive. If you happen to get fc on a drop, fine. But don't spend huge amounts of currency on it. You can get the same dps increase for less currency if you only look for increased spell damage/increased critical stike chance for spells and maybe faster projectiles on a weapon.
Best shields to level up are Kite shields: Ceremonial Kite Shield (available at lvl 34) / Angelic Kite Shield (lvl55) / Archon Kite Shield (lvl 68). The 24 to all resistances help a lot to max resistances. As a life based char an Archon Kite shield may be even a good option for endgame as the low ES doesn't hurt for that kind of build. A CI should better look for high ES shield though.
Update: That advice only holds true for LEGACY kite shields. As of 1.1.0 only kite shields with 12 to all resistance will drop, making them no longer a best-in-slot option while leveling.

CI:
Get as many ES as possible, that means pure ES gear (once you made the transition of course; before that look out for HP on gear as the most important stat). If you are looking for a way to mitigate physical damage use granite flasks. You can’t afford to sacrifice your main “life” pool by wearing armour based gear.
Speaking of flasks: It is important that you have flasks that remove bleeding and dispels burning. Getting punctured or ignited is pretty bad for a CI as your ES will not regenerate. Start running while bleeding and the damage increases resulting in a very quick death. Removes freezing is another mod one of your flask should have. As of 1.1.0 you can encounter the corrupting blood mod on rare monsters. It stacks a bleeding effect on every attack YOU make. Without a remove bleeding flask this is lethal. Same goes for the bleeding stack that Dominus in his last form applies with his cleave attack. Don’t enter that fight without a remove bleeding flask.
Like I said you will need the eye of chayula to avoid stun. Instead of settling with anti-freeze mods on flask many CI chars wear (the very expensive) dream fragments ring that prevents freezing.

Life:
Looking at the colour requirements of the freezing pulse setup (BBRGG) it’s obvious to avoid pure armour and pure ES gear as chest as it would be very hard to get that many off-colours. The best option would be to settle with an evasion/ES hybrid as chest.
The ES would also boost the mana pool with Eldritch Battery. The latter makes a pure ES shield with high ES a good choice. You need a big mana pool to sustain your spells while running auras, heralds and arctic armour late in the game.
You gotta have a flask that removes bleeding (see the info in the CI paragraph above )

Bandit rewards
Normal: help Oak for 40HP when life based; kill all when planning to go CI
Cruel: kill all for the reward point
Merciless: Kill all or help Alira for an extra power charge. Anybody that plans on using power charges should do the latter.

How to handle reflect One way is to use trap - cold snap (or have a fire trap leveled up in your backhand that you can switch to). Traps don't reflect the damage back to you, so no risk using them.
Or use spell totem + summon skeletons for diversion and snipe the aura spreading enemy with ice spear. Be sure it is not linked with LMP you don't want to hit more than 1-2 enemies with it. This works as elemental reflect is not as lethal as physical reflect. The portion that gets reflected back is mitigated by your elemental resist. The damage you suffer is therefore only
damage you dealt * 0.15 * 0.25 (assuming max resist without purity bonus)
In other words with a life or ES pool of only 3000 you would have to deal 80.000 damage to one shoot yourself. Happens only to Discharges that fully blast a huge relect mob.
You should also be able to do maps with elemental reflect as long as you don't spam FP into groups. Shoot once - retreat a bit or snipe 1-2 from the edges.