Build:Ice Assassin

Full Build Details
This build requires the following enchantments and additional passives to function:

Helmet: Inner Cool (10% frost damage)

Body: Spirit of Cierzo (25% frost damage)

(optional) Dagger: Midnight Dance (10% decay damage)

(optional) boots: Flux (3% move speed) or Agis (+1 protection)

(optional) sword: Etherwave (20% elemental vulnerability)

Passive Skill: Lockwell's Revelation

Specialist skills:

Brains (15% more elemental damage, -25% physical)

Patience (25% all weapon skills (including dagger!), -25% physical damage)

The sword is there only for its benefit of 25% more damage for all weapon skills, once again boosting our dagger - any one-handed Damascene or Masterwork weapon can work for this.

with everything listed above, you will have the following numbers for the dagger:

37 base damage

+60% frost damage from enchantments

+50% damage from both the sword and patiance

+45% from passive skills (when very tired)

+30% from cool boon

+50% from elemental vulnerability and Frost Hex

+10% Frost from an Ice Varnish

+15 flat damage from an Ice Varnish

And - 15% frost from the Curropted status effect

For a total of 15+ 260% additional damage (making the dagger's base damage start at 52, before the frost% increase)

your normal dagger slashes will now do 135 damage;

Backstabs are at 540;

Opportunist Stab, when paired with confuse/pain (possible with probe) will do 810(!),

And Serpant's Parry will do 270.

If desired, being in the Heroic Kingdom will also provide a 15% bonus from Alchemical Experiment, bringing the total to a nice 275%

Apart from the strict ice damage, you have both Blood Sigil and Sigil of Wind, along with Conjure ready to provide some covering fire if needed - luring enemies into the blood sigil to slash at them with your dagger will also allow you to apply blood leach, and heal yourself.

If desired, using Pressure Plate Mastery can better set up opportunist's strike, but Stealth Mastery is also a good option to better set up backstabs and have additional mobility. Completely up to preference.