[2.5] Frozen Orb Witch ((Frostbolt+IceNova))

Bandits are all passive points - You could maybe go with cast speed in cruel or a frenzy charge in merc to possibly increase clear speed.

PoEPlanner

Official Tree

Ice Nova - Controlled Destruction - Ice Bite - Cold Pen((Spell Echo if not using pledge of hands)) - Empower/Faster Casting

This is our main clearing skill when combined with Frostbolt, There's plenty of other ways to set it up though. This way is just what I found easiest to use, but throwing in a concentrated effect and/or increased area of effect works well.

Frostbolt - Controlled Destruction - Elemental Focus - Cold Pen - Empower/Faster Casting

Pretty similar setup here, though I honestly haven't tested anything past the 4th link yet. OH CRAP I FORGOT LMP--Wait... No I didn't. If you're at all familiar with Frozen Orb Sorceress you know why I chose to forego multiple projectiles on this. If you aren't familiar though, just know that we have all the AoE we need from Ice Nova.

Orb of Storms - Chain - Curse on Hit - Frostbite

This is what we use for cursing as well as triggering Elemental Overload consistently. Pretty cool, right? :D

Vaal Discipline - Inc Duration - Frost Bomb

This gives us an oh shit button if we're taking heavy damage and need to not die, as well as good cold res debuff for rares(Helps a ton on resistance modded geeks).

Ice Golem - Lightning Golem - Minion Life

More damage and speed as well as meat shields, what more could you ask for?

Discipline//Arctic Armor//Flame Dash//Clarity

This is where things get iffy, because we just don't have enough slots for all this shit. An unset ring is recommended.
Discipline and Arctic armor are great defensive buffs, Flame Dash is used to trigger our cold penetration from ascendancy, and Clarity helps sustain mana.

Tons of options for gear, the only thing I'd say could be mandatory would be Valyrium for dealing with stun. I'm sure there's other ways to deal with this, but this is what I found to be the simplest.

For the rest of your gear, get as much ES/Res as you can on everything. You'll want %cold damage or %cast speed on your jewelry, with %ES also being fantastic on amulets.

There's several pretty sweet uniques we could use on this, but really you could run this almost entirely on rares and be perfectly fine. For shits and giggles, here's the uniques I'm currently using.(Taryn's Shiver is great, though I'm currently using it just to cast portal...)


Flasks are also pretty optional, though I highly recommend at least 1 Quartz and 1 Silver. You should have a staunching and a heat flask somewhere though, like most.
Here's mine, using sapphire flask until I get reduced ele reflect ascendancy.