Welcome to my first build here on Mobafire! I've been lurking around here for quite a bit now, and i think it's time to share with you guys how i usually play Nocturne. He is by far the coolest champion of LoL atm, and probably the most fun champion to play (IMO). I will add more to this build if i feel like it!

Please don't rate if you haven't tried it out yet please? Leave a comment with feedback and suggestions! I'm open to critism if it's constructive and helpful!

(I'm not going to put dates when i changed something here)

Edit 1: Fixed alot of typos
Edit 2: Created an item-switch section (under items)

Pros

+Excellent farmer
+Great damage output in all game-phases
+Awesome ultimate that let's him catch up to those EX-luckers!
+Amazing CC
+Auto-attacker for the most (i always liked auto attackers)
+Awesome passive that let's you stay in lane for SO much longer
+Amazing ganker

Cons

-Can be mana-starved if played incorrectly
-Takes some time to learn when to and when not to use ultimate (Trust me, i've been there)
-Quite squishy, but not Ashe like squishy
-People still call him OP, even though that horrible ulti-nerf.

Here we gooooo
Passive Umbra Blades

Every 10 seconds, Nocturne's next attack strikes surrounding enemies for 120% of his physical damage and heals himself for 15 / 20 / 25 per target hit. Nocturne's basic attacks reduce this cooldown by 1 second.
One of the best passives in the game ATM IMO, harass is more awesomer, great farming tool and great damage dealer. This + Crit in early game is a fkin nuke :)

Q-Spell

Duskbringer

Nocturne throws a shadow blade which deals physical damage 60 / 110 / 160 / 210 / 260 (+0.75 per bonus attack damage), leaves a Dusk Trail, and causes champions who are hit to also leave a Dusk Trail for 5 seconds. While on the trail, Nocturne ignores unit collision and has increased Movement Speed 15% / 20% / 25% / 30% / 35% and Attack Damage 15 / 25 / 35 / 45 / 55.

It has been nerfed, but still awesome. Use for farming, attacking, escaping, checking dragon/baron, checking brushes, chase, and more actually. This is your MUST spell when your attacking someone (if they're at not low health). Just think when using it to farm and harass early game (or both in one shot), because it eats alot of mana.

W-Spell

Shroud of Darkness

Nocturne empowers his blades, passively gaining attack speed 20% / 25% / 30% / 35% / 40%. Activating Shroud of Darkness allows Nocturne to fade into the shadows, creating a magical barrier for 2 seconds which blocks a single enemy ability and doubles his passive attack speed for 5 seconds if successful.

This is what makes Nocturne the Anti-All champion. Deny, deny, deny and deny even more! If you deny in the most awesome way, you do have the rights to yell DENIED to the other team. Especially after destroying that Nunu & Willump after you blocked his ultimate. You earned it!
Oh and it gives a nice AS passive.

E-Spell Unspeakable Horror
Nocturne plants a nightmare into his target's mind, dealing damage each second for total 50 / 100 / 150 / 200 / 250 (+100% of ability power) over 2 seconds and fearing the target for 1 / 1.25 / 1.5 / 1.75 / 2 seconds if they do not get out of range by the end of the duration.
This is what makes Nocturne such an amazing auto-attacker. But i don't really max it until the end since i never felt that the fear effect has to be longer, and the damage isn't really that needed to, since it fuels by AP.

And finnaly. Your ultimate. Paranoia

Nocturne reduces the sight radius of all enemy champions and removes their ally vision for 4 seconds, this includes champions, minions, wards and towers. He can then launch himself at a enemy champion with a large range 2500 / 3250 / 4000. Deals 150 / 300 / 450 (+1.2 per bonus attack damage) physical damage on arrival.

THIS is what makes Nocturne Nocturne. This is your bread and butter. This is your 3v3 dominator. This is SPAA- i mean Paranoia. It makes your oppenents almost completely blind. They cannot see anything except for a few metres around them. And best of all, they pretty much **** their pants if you attack them.

Scenario time!

Low-HP oppenent hammering your turret? Nuh-uh.
Lucker getting away with low hp? Nuh-uh. (gotta love diving)
Your far away from a teamfight, and you see a low-HP opponent? Get in there and shake that teamfight around!

Time to learn how to attack!

If your laning opponent over-extends?
Duskbringer> Unspeakable Horror>hammer hammer hammer>Ignite>Dead Hopefully, if not, Paranoia him when his at his tower, BAM dead. (Use Clairvoyance if you have it and need it.

Ganking?

Paranoia in and throw down Duskbringer and get that Unspeakable Horror on. Then just hammer hammer hammer, and ignite if you have it.

Skill Sequence explanation!
Duskbringer at level 1, why? Easier FB, skillshot to check brush + sniping.
Shroud of Darkness at level 2, you just gotta love denying those Nidalee's spears, Katarina's knifes right?

NOTE that this skill also block ultimates!

Nunu & Willump's ultimate? Pff, just childplay to block that one.
Karthus's annoying-*** ultimate? Pff, lucker Nocturne doesn't exist, skill Nocturne does exist.
Ashe or Ezreal's last-hitter ultimates? DENIED.
Oh yeah, blocking Akali's ultimate make her do the flying animation without flying to you, kinda hilarious to watch.

Level 3, Duskbringer/ Unspeakable Horror if you feel that you need it.

Level 4, Unspeakable Horror if you haven't trained it in level 3 of course, then it's Duskbringer Here.

Level 5 Duskbringer. MOAR

Level 6 Paranoia YES YES get your ganking-glasses on and gank mid-lane!

Level 7-18, Follow build.

So there are a couple things i would like to point out regarding my chosen summoner spells at the top, they are not the most recommended, maybe not even the most beneficial. But that's what i usually roll with.
Other choices are
Clairvoyance - Great if you just lost vision of those low-hp luckers.
Exhaust - Great for those fast *** champions or blinkers like Ezreal and Kassadin
Ghost - I don't usually take this, since my Duskbringer has an similar effect.
Heal - If you are a new player, or just wanna be a complete douchebag this is your prime choice.

Meh spells
Fortify - your not the tank, i hope.
Clarity - If you are having EXTREME mana issues, take this until you learn how to play him correctly.
Cleanse - If you can't live without this, and hate getting CC'd, go ahead.
Smite If you are jungling, yes.
Teleport Soloing? Take it.

Prohibited spells
Revive - No
Rally - No

I like to go 21/0/9, because i play quite offensive. Sometimes 21/9/0 if i feel that im getting hammered as **** on my lane. (It happened twice, OK?!)

There we go, masteries done, moving on.

Im going mostly offensive here with my items.
You will start with Doran's Blade, it help me stay in lane so much longer with my Umbra Blades to get myself some HP. Remember that you can sell this for an extra slot when you need it later on in the game.

Second is Boots and a couple of wards or potions, which i build into Berserker Greaves a ASAP (They're quite cheap)

Third, is Sword of the Occult because i usually have 4-10 kills by mid-end of mid-game. If your feeling confident, or getting fed as **** already, you can get this right after your Boots, since it will make you much more stronger, and scarier later on.

Fourth is... The Brutalizer, because it gives a bit off damage, some CDR and a nice bit of armor penetration. We build this into Youmuu's Ghostblade later.]You can get 2 Vampiric Scepters after your Brutalizer here, i've noticed it helps me alot with that bit more lifesteal. Builds into Bloodthirster later.

Fifth Banshee's Veil Because it gives a nice shield every 45 second, which works great with your own spellblock, and gives some nice Magic Resist. You can switch this for a Thornmail if you are meeting a heavy Auto-attack team, like Master Yi or Tryndamere, or if you get focused by an AD-Carry. It will make them cry, and definately not focus you first.

After that, Youmuu's Ghostblade, it gives a little bit more gold, crit, and more Armpen and CDR. It also comes packed with an awesome active ability which you should use whenever you get the chance.

If you manage to comes this far, Bloodthirster for lifesteal and great damage (if stacked up).

Item switch-up

If your new with Nocturne, or just bad this is the section for you.

or
This helps alot with that sexy Armor penetration you get from the Last Whisper.
I even this against teams with heavy tanky/tank features instead of Occult, since it helps me and my team with bringing down those douchebags.

- -
I strongly don't suggest taking anything else then the , since Nocturne is an auto-attacker at heart. You might pick against a CC heavy/AP Nuker team, or if you're going against another , or .

Time for a rune-quicky!

Greater mark of desolation, I'm offensive, as i stated numerous times now.
Greater Mark of Attack Speed, if you are a real AS Who-, i mean a real AS kind of guy. Still don't these are as beneficial as the ArmPen ones.

Greater Glyph of Replenishment, More mana-reg, more harassing + farming with Dusk Bringer.

Greater Seal of Evasion, it's just great on meelee's, it has saved my *** plenty off times now.

Greater Quintessence of Desolation, MOAR ARMOR PENETRAATIOOONN NAAOO