I typed this up to help someone that was having trouble staying alive on his Nightblade and figured it couldn't hurt to put it up in the Player Guides section as well. I'm currently a fair way into Veteran 3 with this build and haven't run into any problems yet. Feel free to provide feedback and suggestions.
Shrunk url out of necessity. That's my basic build and you can get it rolling very early on.
Slot 1: Puncture
(1h/shield), morphed to Pierce Armor
. Originally the skill only lowers the target's armor. The morph makes it lower spell resist too. This makes your leech do more damage, and the health returned is based on damage dealt. It's a small amount but every bit helps. Also, this skill is great in groups because since you are debuffing the mob instead of buffing yourself it ups everyone's damage.
Slot 2: Low Slash
(1h/shield), morphed to Deep Slash
. The original skill here lowers the target's weapon damage. The morph makes it lower ALL damage. Very useful, especially when you already have decent mitigation from heavy armor and blocking.
*note* If you absolutely must have a dash attack of some sort, I'd use Shield Charge in place of Deep Slash. Pierce Armor is the more valuable of your weapon skills. You may be built like a tank but you are still a Nightblade, and it helps you deal more damage. Personally I tried Shield Charge for a while and just didn't see much need for it in PvE. It's stamina heavy and can't be used point blank.
Slot 3: Strife
(Siphon), morphed to Swallow Soul
. The morph gives you a buff to all healing received, at all times while slotted. This skill is going to account for most of your magicka usage, as the only other magicka skills you have are an opener and a finisher. During easy content I use it for damage. On harder fights I make sure I keep the heal going. Also, remember that you can cast this spell from behind your shield while blocking.
On that note, install this mod. --- http://tamrielfoundry.com/ftc/
It will let you see when your buffs and debuffs are up and how long they have left. Useful for all three of the skills I just covered. Also alerts when mobs enter "low HP" for the next skill...
Slot 4: Assassin's Blade
(Assassin), morphed to Killer's Blade
. This is your finishing move (deals more damage when mob is below 25% hp). The morph makes it also restore 15% of your HP on kills (up to 18% later). There is also a passive in the same line that makes kills with skills from this line give you mana back, making this finishing move basically give you back its casting cost. This skill is invaluable when charging into a large group of mobs. It also makes that last 25% on bosses a breeze.
Slot 5: Veiled Strike
(Shadow), morphed to Concealed Weapon
. The morph here just gives you a movement speed buff while sneaking at all times. I just liked the convenience of it, as the other morph is an armor debuff and we already have that covered with our first skill. The major note of this skill actually comes with the basic skill; the large stun when executed from stealth.
I will note that I am a khajiit in heavy armor, and the racial stealth bonus allows me to successfully use sneak attacks without relying on the medium armor passive to get stealth radius down. If you wont be using stealth, swap in whatever you want for this 5th ability. Honestly, for the first 40 levels or so I just used the 5th slot to dump in skills that I wanted to level up.
Originally the 5th slot was going to be for Summon Shade > Dark Shades
, but I am still not there at level 50 (unlocks at Shadow 42) since I didn't have a Shadow skill slotted for a very long time while leveling. I have read that the damage on Summon Shade is horrible, but I am honestly more interested in stacking the 15% damage debuff with Deep Slash (the second skill up there), which also has a 15% damage debuff.
Ultimate: Soul Shred
, morphed to Soul Tether
. The damage is good, the stun is wonderful for those large pulls, and the single target effect is a nice bonus when you pop it during boss fights. The ultimate cost is 150, which isn't too bad for the return. It's also your only AoE.
For my mundis stone effect I went for Spell Resist and didn't look back. You'll be hitting the Armor softcap already while leveling in heavy armor, and spell damage is everywhere. After I got up over level 40 and started making heavy use of stealth attacks I ended up swapping it for movement speed. That's purely convenience though.
Lately I've been making heavy use of Concealed Weapon. I will take down the first mob in a group in three hits in most cases. Concealed Weapon (from stealth), heavy attack, Killer's Blade. This uses zero stamina, and your Executioner
passive from the Assassin line means that you will start rapidly regaining magicka when the first mob goes down.
For the rest of the mobs, or from the start if I'm just running in, I open with Pierce Armor. This makes sure that all of the attacks that follow take advantage of the armor/resist debuff that it puts on the mob. If I feel the need I slap on Deep Slash to deal a bit of damage and to debuff the mob's damage. If I don't feel that the debuff is needed I skip right to Swallow Soul and get that HoT (Heal Over Time) going. If it's going to be a longer fight, from this point on I merely keep my HoT going and keep the mob debuffed. I use basic light and heavy attacks for damage until the mob gets below 25% health and I can use Killer's Blade to finish them off. For easy fights just mash your face on the keyboard as needed. You'll live.
Another note, use your bash (click attack while holding block) often. As soon as you see the red marks around a mob showing a spell being cast, bash the living hell out of that mob. Doesn't matter what the spell is. Run across the combat zone if you have too. With the 1h/shield passives your bash is a beast, and mobs casting never ends well for you. Also block all heavy attacks, but resist the urge to slam the mob down while it is dazed unless you want to focus on that mob or it is already your target. You are a single target character, and taking mobs down one at a time is more effective than bouncing between them. Let the mob stand there swaying on its feet while you go back to whatever mob you were already killing, or switch fully to it. Don't bounce between mobs.