I've got in idea on a Magicka-related Nightblade caster build. It is quite simple but I'd like to hear some advices on the possible improvements and may be reasonable critics. The main idea is putting the maximum damage possible against a single target in PvE. It makes it good for Dungeons, Questing and leveling. Also it is very easy in use.

So here are the skills for your main bar:

1. Strife/Funnel Health/Swallow Soul
2. Mark Target/Reaping Mark
3. Magelight/Inner Light
4. Entropy/Degeneration/Structured Entropy
5. Grim Focus/Merciless Resolve


Now how it will work in theory. We will use ranged weapons; we will put our points hard in Magicka and will wear +Magicka equip.
That will make our primary nuke - Strife hit for a reasonable amount of damage. It is by far the best Mana nuke available for Nightblades. Even if it has no big numbers in a tooltip but it is very mana-efficent. For now I am dealing nearly 3 damage for 1 mana spent, plain and simple. Cannot pull anything close to it with any other abilities available. Ofc Assasin's Blade is even more efficient manawise when the Health of the target is low, but enemies doesn't run around with half-empty healthbars you know.. We need a universal nuke and that is Strife. Also it has a good animation which helps us in spamming it and also it sustains us with a minor but nice HoT, which will be always up in combat.
Choosing the Morph is not a bid deal here. More solo = Swallow soul, more grouping = Funnel Health. I prefer second.

I strongly recommend to use either Macro (as I do using my mouse software) or your swift fingers to mix your Strife spam with Light attacks. The idea is to interrupt Light attack animation with a Strife cast and send Strife and staff projectile simultaneously. It improves overall DPS (as it does not interfere into Strife spam, and only adds our Light attacks as bonus) and also feeds our Grim Focus, but more on that one later. In short just kill the enemies with: Light attack, Strife, Light attack, Strife, Light attack, Strife, Light attack, Strife, Light attack, Strife..

All other skills on the bar aims for only one purpose - improve our main nuke even more.
Mark Target will tear the magical defenses of the target improving Strife's dps. Our allies will benefit from it as well. Even the physical damagers will like it, as armor is also decreased with that spell. And it will heal us a great deal when the target is dead. That happens quite often when clearing the trash in dungeons and soloing. Less of a note when fighting bosses, but they may have adds and anyway we have some other healing options in our list (including pocket healers in dungeons:) ). There is also a Weakness to Elements option from the Destruction stuff to lower spell resistance of a target but it is worse by far. Most important thing is - Mark Target could be cast before combat without engaging the enemy. It doesn't even break stealth. So you may cast it as a preparation. The range is twice as large compared to Weakness so it is easier in use. Also Weakness does not heal you, and doesn't lower armor.. The only (and very minor) benefits of Weakness are the 0 mana cost and the ability to get you some mana from your attacks. I don't think mana will be such an issue with a cheap Strife nuke. But see for yourself..
Improve Mark target only with Reaping Mark - it will increase your DPS a little bit, while the other morph is for PvP to catch stealthers in Cyrodiil.
So we should start the battle with Mark Target - it won't provoke anyone and we start the fight with its bonuses already.

Magelight/Inner Light - always on. Very simple thing - it does not require any usage in combat. It is just there on your bar and improves your crit chance. Inner light effect also increases your magicka (while unmorphed version decreases it, so get morph ASAP). More magicka = more damage for a Strife.. Nothing here to add, except "don't bother with other morph - it is for PvP as well"

Entropy/Degeneration/Structured Entropy - pimp your ride nuke even more. Major Sorcery effect is +20% spelldmg - that is what we need. Also it adds a minor DoT on an enemy target which is nice to have compared to the absence of it. And it will heal us as well. Minor heal for you on cast, and every 6 sec after it, while the effect is active and the target is alive. So we already have a Strife, Entropy (and Mark Target from time to time) selfheals. They are not strong but persistent - improves your survivability a great deal.
Keep the effect (buff on you) always on from the begining of combat, recast when it wears off. Check for visual effect or use the addon (I use the FTC).
Choose the morph at your taste. Generally the Structured Entropy option is better (+% hp as long as it is slotted) on a highest levels as it helps us to get to the needed Health threshold (around 20k for now) with fewer points put in Health. And those saved points may go directly to our mana pool improving our DPS even more. But Degeneration is ok if you feel you need EVEN MORE selfheal (for what?). Light attacks will be spammed by us persistently so it will feed you with even more minor heals.
Yeah, and Sap Essence alternative from the Siphoning tree (also grants Major Sorcery) won't do IMO, as it is melee range. But as we lack AoE in this build, you may want to consider that as well. Also if you use a Bow for some reason (in Magicka build, really?) weapon damage buff may seduce you to the dark side of Sap Essence. But I vote for Entropy. MaxHP bonus and Hots and DoTs overweights..

So now we have bonuses to spellcrit, spelldamage, mana from our other abilities, and the magical defenses of a target is nullified. Let's just go berserker now

Grim Focus/Merciless Resolve gives you a +8% berserker buff to all your damage. It perfectly stacks with all others buffs we have and is a cherry on the top of that DPSing pie But more than that. If you heeded my warning and used a strife+l.attack mix in your rotation (see the Strife section for details, and that is a must for maximum DPS) you will occasionally (and automatically) pop a powerful attack (after every 7 light attacks). In addition to the havoc you've already wrecked upon the enemies. Just keep the buff up. Merciless Resolve morph only - because we need no stamina from the other morph and we need moar DPS.

Ultimate - at your will. Consider Death Stroke - nice singletarget damaging ability, also it grants additional damage to the target for a few seconds, and that debuff stacks with Mark Target debuff. It is melee, but every once in a while we may let ourselves to run into an enemy. Also it is quite cheap and may be used often. Incapacitating Strike morph won't do as we have too many HoTs on us meaning we are almost always at fullHP, so take Soul Harvest. Go, go - spam Ultimate

TL;DR:
So imagine - enemy is debuffed with Reaping Mark and you are buffed with Inner Light and Merciless Resolve upfront. Fight haven't even started yet and such an advantage worked out. You open with a Heavy attack (for example) and then cast Structured Entropy and start spamming cheap and powerful (by now) Light attack + Strife simultaneously and infinitely. Actually this one-button-spam is all you need further in a fight. Keep the effects presented up if it is a long battle ofc.
end of TL;DR

For now I am trying to figure out how to not let the overlapping of Minor and Major Berserk effects from Merciless Resolve (minor, long) and Reaping Mark (major, short) - it doesn't look that effective, though it is not a big issue and may be ignored.

Any ideas on that build?