Adapted from
http://elderblade.enjin.com/forum/m/28903347/viewthread/22887609-meteor-factory-magicka-nightblade-build

Can put all attribute points into magicka if confident of survival. If not, try for around 17-18k health points for most group situations.

Mundus Stone
If you have at least 2500 spell power without the Apprentice, switch to the Thief. If not, Apprentice or Mage would probably be best.

Gear
Medium Molag Kena's Mask - Divines - Max Magicka
Heavy Cuirass of Julianos - Divines - Max Magicka
Light Molag Kena's Epaulets - Divines - Max Magicka
Light Gloves of Julianos - Divines - Max Magicka
Light Breeches of Julianos - Divines - Max Magicka
Light Sash of Julianos- Divines - Max Magicka
Light Shoes of Julianos - Divines - Max Magicka

Can use Magnus' Gift in place of Molag Kena/Torug's Pact for lower levels.

Willpower Necklace - Arcane - Spell Damage Enchant
2x Willpower Ring - Arcane - Spell Damage Enchant

EITHER:

Maelstrom Destro Staff
OR
Inferno Staff - Nirnhoned - Poison Damage Enchant
AND
Inferno Staff - Nirnhoned - Prismatic Enchant (for use against daedra/undead)

2x Sword of Torug's Pact - Nirnhoned - No enchant needed, you'll never be light attacking with these

Without a Maelstrom Staff (I don't have one, either), you'll have a dead slot as far as set bonuses are concerned, but at least you can get a nirnhoned staff in there to help break spell resistances. You may also consider running a sharpened staff for trash pulls.

Destruction Staff

#1 - Merciless Resolve - Grants Minor Berserk for 20 seconds. While that's happening, your medium attack weaves are racking up four successive hits to proc Assassin's Will. Once you use the proc, put it right back up.

#2 - Funnel Health - This will be your main nuke. Medium weave to land some respectable crits and siphon 26% of the damage dealt to yourself and two nearby allies every two seconds.

#3 - Crippling Grasp - Your main DoT. Not only does it steal any enemy's movement speed, but it gives the stolen amount to you in the form of Major Expedition. This goes a long way towards not standing in stupid.

**#4 - Flex slot**
Use one of the following skills

Rearming Trap - I had no idea how amazing this skill was until recently, and it's now a mainstay on my single target bar. It deals magic damage, but costs stamina(!). Most importantly, it provides 12 seconds (6+6 when it rearms) of Minor Force, increasing the damage dealt by ALL critical hits by 12%. You may have noticed that you crit a LOT. Making those crits deal 12% more damage is like Christmas. Once the 2nd 6-second minor buff wears off, immediately reapply it while keeping up Crippling Grasp.

Elemental Blockade - I will swap this out for Rearming Trap on trash pulls or any AoE fight. It deals magic damage and is a delightful complement to Twisting Path. It can be rapidly swap-cancelled to shift to your back bar, where you'll then lay down a Twisting Path and start the Sap spam.

Shadow Image - Awesome skill. Damage scales off thaumaturge, and it can be used as an emergency blink out of red. I will typically run this on a Manti burn, as it allows you to rapidly blink back after "popcorn" or after evading the portal. Its other morph...

Dark Shades - ...is also pretty cool. It debuffs the enemy with Minor Maim, and the two of them will deal more DoT than Shadow Image. The problem I see with this morph is that if we are at range, which we will usually be when not in stacking fights (trials), the time spent for the two shades to close the gap is wasted DPS. Furthermore, their proximity to the fight means they're more likely to be stunned, again wasting DPS. I would leave this to the Nightblade tanks, but if you're confident that you'll be staying in melee range (Stone Atronach, Manti burn, The Serpent), I can see the advantage.

Structured Entropy - More DoTs + health + Major Sorcery. Use this while leveling up, or if you're not doing content worth blowing spell power pots on.

Piercing Mark - The main reason you'll want it slotted is that it increases your critical chance from the Pressure Points passive. Nevertheless, I would only slot it on fights where the boss is not going to be getting Major Fracture and Major Breach from other sources, namely the tank's Pierce Armor or the healer's Elemental Drain.

#5 - Inner Light - You know why.

Ultimate - Ice Comet - Since we're not DKs and don't care about Fire damage, the Cold damage change is unimportant. The extra ultimate generated by Shooting Star is unnecessary for us, as in AoE situations will have already swapped to our dual wield bars and have Soul Harvest's passive active. Ultimately this is the better morph for single-target fights.

Dual Wield

#1 - Sap Essence - Your main AoE nuke. The more enemies the better, because its damage scales based on how many targets it affects. Grants Major Sorcery and Major Brutality, steals health for you and your allies.

For single target fights, go ahead and switch this over to Merciless Resolve. It's easier to keep the buff active during the execute phase, and more Assassination abilities translates to more crit rating. More crits proc Hemorrhage, granting Minor Savagery to all nearby allies.

#2 - Impale - Execute. Spam the hell out of it starting at about 25%. Don't bother to weave. Make sure to keep Merciless Resolve up while executing.

#3 - Twisting Path (Refreshing Path) - AoE DoT. Procs Siphoning Attacks, and when used in conjunction with Elemental Blockade on big pulls your AoE DPS will be massive.

On a single target fight, I would slot Piercing Mark just to increase your crit from the Pressure Points passive.

**NOTE** - I have heard from several sources that Magicka Detonation is absolutely BANANAS in lieu of putting up the Path. I do not know from experience, as I am allergic to PvP and don't have a high enough Alliance rank to get it.

#4 - Siphoning Attacks - Keep it up during your Sap spamming or you'll run out of magicka very quickly. It's not hard to weave it in when you're reapplying Twisting Path.

Again, swap this out for single target fights, as this bar will really only come out during the execute phase. I put Rearming Trap here to ensure I can keep up Minor Force during the execute phase as well. I've achieved 45k Impales unbuffed on my own, so with Warhorn and Minor Sorcery (Templar's Illuminate passive), 50k surely isn't far off.

This slot is also where I put my Magicka dump (Siege Shield) for the Serpent fight.

Inner Light - See above.

Ultimate - Soul Harvest - I adore this skill. It's not just about charging our Ultimate on trash pulls. It deals good damage that scales off Thaumaturge, it's dirt cheap, and Major Defile's alright. The 20% increase to your damage will make your Impales amazing.

This can be somewhat problematic to use on fights like Valariel, where there's a surplus of melee DPS that you don't want to crowd, or there's stupid that you can't stand in between the boss and you. If the opportunity presents itself, close the gap while executing and smack it. Sometimes you may be called to slot Veil of Blades for the mitigation. It really depends on the situation.

Rotation

Single Target
Pre-buff with Merciless Resolve. Fully-charged Heavy Attack -> Rearming Trap -> Medium Weave (MW) Crippling Grasp -> MW Funnel Health until Assassin's Will procs, then use the proc -> Reapply Merciless Resolve -> MW Crippling Grasp -> MW Funnel Health. Closely monitor your buff tracker to see when to reapply a Rearming Trap and continue until execute phase, at which point you swap to your back bar and light it up with Impale. Make sure to keep Merciless Resolve and Rearming Trap active for Minor Berserk and Minor Force.

AoE
Pre-buff with Merciless Resolve and Siphoning Attacks. As you approach, drop your Ice Comet and lay down Elemental Blockade, quickly swap-cancelling it to your back bar. (If the mobs aren't yet stacked up, you may choose to wait on dropping the Ice Comet until they are). Lay down Twisting Path and begin to spam Sap Essence, stopping only to reapply Merciless Resolve and Siphoning Attacks. Reapply Twisting Path / Siphoning Attacks if the fight carries on, but I usually find that switching back to your front bar to lay down another Elemental Blockade is wasted DPS.