@SickTwistedSmile: Attack Speed is a must, get it on the costume affixes and on the Artifacts if you can. Alternatively, you can replace one of the artifacts for a Scroll of Pama, if you're having spirit issues. This is helping for leveling but by 40+ you really shouldn't be having spirit issues. Other than that, gear is really up to you. This is a very versatile build and stat-wise, you can work her however you prefer. For my own Scarlet, I gave her armor, hp regen and +mental damage gear for added survivability, and if you can find gear with a few bonus points in Bewildering Hex, you can increase the time spent confused without adding more power points to it. With the radius provided by medal + artifact, Confusion will hit nearly everything you could want it to.
NOTE: Outdated, updated videos TBA
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2.05 Update:
With the big December patch bringing everyones TTK/TTL (time to kill/time to live) within range of each other, people now have more elbow room for their builds in regards of killing enemies within a respectable amount of time. This along with some changes to Wanda's skills have changed this build fairly significantly. TL;DR version is: Switched medal to Cthonic, switched Relic to Gibborim, changed final two artis, removed points from Bewitching and CM for Ominous and Ruinous, removed Chaos Warp, and Enfeebling has been changed to a powerful passive named 'Obfuscate'. In the case of the latter, the calculator hasn't been updated to reflect that change yet. Though the names are different however, both Obfuscate and Enfeebling share the same position and icon, so it shouldn't be too confusing.
Like my other builds, this rendition of the Witch is created to handle multiple situations. She has powerful AoE DoTs, debuffs, reflections and great single-target DPS thanks to the combination of DoTs like Combustion Hex and the unrelenting damage from Chaotic Hex.
Combo:
Reality Imposion, Enervating Hex, Combustion Hex, Ravenous Binding, Chaotic Hex spam until dead. On bosses, set Corrosive Hex and Entropic up as necessary.
Powers:
Combustion Hex - So much damage in this AoE, and Wanda gets it early into the build as well. Get it, love it.
Chaotic Hex - More for single-target dps. Extremely powerful and normally eats Spirit, but this build has almost no Spirit issues. You'll be at 400+ spirit and orbs should keep your Spirit high almost all of the time. Very few things will be able to survive long enough for your spirit to ever deplete.
Bewitching Hex - This is your Basic. Gives spirit back, and with DPS patch, doesn't require a huge point investment to hit hard. Primarily a means of regening during boss fights.
Ruinous Flux - DPS patch has changed this to be a fairly effective means of DPS, and with her greatly improved durability thanks to massive amounts of regen and projectile deflect, she can teleport into crowds and survive just fine while this ticks away at their health AND procs effects from Cthonic, Mandarin and Entropy gloves.
Reality Implosion - Used more for its utility. Realistically you can switch out 4 points in this skill for anything else you'd prefer, I just like numbers that end in either 0 or 5...bit of ocd.
Enervating Hex - Recent patch has made this an awesome skill. It's a hard-hitting AoE now that also stuns everything it hits. This should be a part of nearly every Wanda's skill chain, it improves her survival greatly.
Corrosive Hex - One point is enough. Weakness and Vulnerability have been standardized to a flat 10% modifier, so more ranks in this skill will only improve duration. You'd be better off just recasting it. Only necessary for bosses.
Obfuscate - previously called 'Enfeebling Veil', this is now a passive (calculator is a bit out-dated atm), raising Wanda's Projectile Evasion and base defense. Sexy.
Entropic Warding - One point alone will suffice. This skill used to be vital. That has changed with the patch, and you'll be using this skill more strategically for specific fights rather than as a precursor to every single one.
Chaos Magic - Adds a bunch of different debuff effects AND max spirit. Get it, love it.
Hex Binding - 1 point wonder, get it just to access Ravenous.
Chaos Shift - A recent addition to the Witch's arsenal, this is a (much needed) teleportation skill. Patch has changed distance of teleports and standardized them, so only 1 point is needed now. Additional points raise the burst damage, and you're already doing plenty of that.
Winds of Chaos - 1 point. Obvious skill is obvious.
Cthonic Gloom - 1 point to open up the next skill.
Ominous Veil - this skill was changed with the recent update to be just...fricken amazing. Not only was the fear changed to a cower instead of a flee (effectivelly functioning now as a long-duration stun), it now also comes with projectile evasion. USE IT.
Ravenous Binding - The bread and butter to the Dark Queen build. Not only is there huge amounts of damage coming from this skill, it also immobilizes AND restores Scarlet's health.
Gear:
Relic of Gibborim - This build already has tons of damage and survivability, so I opted instead for Gibborim. This allows you to spam Chaotic Hex for insane amounts of time while your various DoTs tick away at enemy health.
Pluvian Superconductor - AoE damage, get it.
Mark of the Odinborn - Keeps your spirit high, regen spirit whenever you pick up an orb (including exp orbs)
Cthonic Idol - great artifact for procs, as your DoTs have a constant change to proc this and other pieces of equipment like it.
Binding Brazier - the proc is only so-so, the real fun here is the boost to damage rating against burning enemies, and with a 20+% chance to proc, this means you'll have that bonus fairly often.
Costume:
Core - +1 Energy is obvious. If you can get 25% regen AND lifesteal on this core, consider yourself extremely fortunate. It's rare and difficult, but possible. One or the other is sufficient until you get both, however.
Affixes - Damage rating all the way. May, however, want to consider attack speed for the third affix while looking for some to add through gear, just to speed up a few animations. Not critical, but helpful.
Additional aims for equipment: Health and Spirit on hit/kill are helpful, as is mental damage. If you are going to try and +any skill to 35-40, the first priority should be Ravenous. One of the first priorities should be to get Wanda's 'Gloves of Infinite Entropy', as it really sends this build through the roof.