Sneak Build for Cheesing Black Sacraments and Heists - Nachtklinge Baue PvE - ESO

• Subclassing
• Gear
• Active skills
• Extra passives

This build is designed for max movement speed while sneaking and keeping up Shadowy Disguise. Do not use this in combat (dungeons, etc.) as you will do no damage.

This build is over-provisioned in terms of speed, max magicka, magicka regen and minimal detection radius, meaning you're able to replace some skills/gear pieces without breaking the build. 

Subclassing

The only class skill line that's essential is Shadow for Shadowy Disguise. The other two are completely optional, but can offer some small bonuses: Restoring Light is used for the slotted bonus of Repentance, Dark Magic is used for its cost reduction passive. Use one of your class skill lines in this slot if your character isn't a Nightblade, Templar or Sorcerer.

Gear

• Vesture of Darloc Brae reduces the detection radius and gives a massive sustain boost.
• Night Terror also reduces the detection radius. This build only needs the 3-piece bonus.
• Ring of the Wild Hunt gives a massive speed boost.
• The single piece of Magma Incarnate offers double recovery which is nice, but can be easily replaced with another 1-piece bonus (e.g. only magicka recovery, max magicka).
• Greatsword offers the best passive bonus for this build, but a battle axe or maul are also fine. You do need a two handed weapon for the active skill Rally.
• The body traits/enchants are all Infused/Max Magicka for Shadowy Disguise uptime. 
• The Magicka Recovery glyphs on jewelry also help with magicka sustain (when recovery kicks in when standing still). Reduce Spell Cost glyphs don't work on Shadowy Disguise as of Update 46. The Infused trait boosts recovery, Swift boosts speed. Run more Swift if you're missing other speed buffs.
• The Trainee pieces are used to fill in the gaps and for some extra resources. These can be replaced with two pieces of Druid's Braid or any other two pieces with a useful bonus.
• The weapon trait/enchant doesn't matter, I recommend slotting a poison for the Dark Brotherhood daily quest (e.g. random trash poison or the ones from the daily rewards). Powered is the only trait that can be useful outside combat.

Active skills

• Shadowy Disguise is Shadowy Disguise. You cannot be seen.
• Spell Symmetry is used to exchange health for magicka for infinite magicka sustain as long as you can heal yourself. Using this skill does not break stealth/Shadowy Disguise. Keep in mind that higher vampire stages reduce or halt your natural health recovery.
• Rally is used for the healing effect to offset Spell Symmetry's health cost. Using this skill does not break stealth/Shadowy Disguise. Keep in mind that the healing effect triggers when Rally ends, meaning you have to press it twice if you don't have the skill already active. 
• Inner Light is slotted for its Max Magicka buff and Mages Guild passives.
• Elusive Mist can be used as a movement/escape tool. Keep in mind that it's a Criminal Act.
• Barrier is slotted for the Magicka Aid passive in Support. You can also slot the Shadow ultimate here and for some extra class passive buffs.
• Repentance is slotted on the backbar for the 'while slotted on either bar' bonus (extra recovery). You don't have to activate it.

Extra passives

• Shadow passives help with recovery.
• Dark Magic's Unholy Knowledge passive helps with sustain.
• Restoring Light's Mending passive strengthens Rally's heal.
• Light and Medium Armor passives help with sustain/recovery and movement speed.
• Two Handed's Heavy Weapons gives you some extra spell and weapon damage for having a greatsword equipped (strengthens Rally's heal). Balanced Blade reduces Rally's cost.
• Vampire is useful for the Dark Stalker passive, specifically the ‘Ignore the Movement Speed penalty of Sneak’ part. I do not recommend using high Vampire Stages for the other passives: you don't need them for this build, but you do need health recovery.
• Race doesn't really matter, Khajiit and Wood Elf have useful sneaking/thieving passives.
• Legerdemain's Improved Hiding passive helps with sustain.
• Dark Brotherhood and Thieves Guild add some flavor.