1. There is no solid item build here, so I listed the items in a generic timeline including all branches. Read at least the item section before playing.

2. I am not liable for you trying to use this build without the proper runes. Feed at your own risk.

This is a guide to Nocturne as a jungle tank with high cc and killing power. The overall goal is to maximize survivability so you can train targets with slows until they die. Once teamfights come around, your ult and CC will allow you to completely disable their carry, and probably kill them. As an extra bonus, you can safely tower dive a lot.

Runes are designed to allow you to avoid rushing heavy armor/MR items.

I recognize that other playstyles work for this champion, so please don't downrate this guide because you prefer them.

Pros:
-Near unkillable
-Extreme CC
-Great initiator
-Easy farming
-High uptime
-Doesn't require kills to be effective
-Near guaranteed win if the match reaches lategame
-Build can be adjusted to counter single enemy legendaries

Cons:
-Low-moderate DPS
-Map awareness is a must
-Dependant on team being good at dps
-Has trouble solo killing
-Most people are convinced that Nocturne is a dps champion, and will probably want to play him that way, so you might get raged at for taking him and tanking.
-High skill cap on Duskbringer shots

My rune setup is designed to maximize defense without buying any heavy-armor/resist items. Some other rune setups may work as well, so I will list what else is almost-good here.

Marks:

greater mark of desolation ARMOR PENETRATION:
-Best physical marks, period.

Seals:

greater seal of defense ARMOR PER LEVEL:
Armor is good. It makes you laugh at towers. Flat armor runes are not worth using, since you match them by level 9. I use these as part of my overall strategy of stacking health items and defense runes.

DODGE:
If you don't have armor per level runes, you can use these, as they are nearly as good (but not good enough). They stack multiplicatively with Ninja Tabi or evasion, or else they would be considerable.

greater seal of vitality HEALTH PER LEVEL:
About half as effective as armor/lvl seals, but the third best option if you don't own the runes above.

MAGIC RESIST PER LEVEL:
If you play ranked, it might be a good idea to back-book (have an extra rune page set) with these. They are only effective if you know that the other team has no physical dps, but very strong if you can catch that.

Glyphs:

MAGIC RESIST PER LEVEL:
No other glyphs compare to these in power. The magic resist is extremely high, and all other glyphs suck for Nocturne.

Quintessences:

greater quintessence of defense ARMOR PER LEVEL:
My personal choice, since the rest of the build is focused around endgame anyway. These are really nice for tower diving mid-game, and just as good as flat armor by level 12. This is the only rune set up for debate.

ARMOR:
Like armor/lvl runes, but help early game a lot and barely weaken late game. I use one of these to solidify my level 1-3 jungle.

MAGIC RESIST PER LEVEL:
Great defense against mages. Another rune I would suggest back-booking if you play ranked.

DODGE:
A good option if you don't have armor runes.

ATTACK SPEED:
Very strong offense runes, much moreso than arpen on tank Nocturne. If you don't have any of the other runes, or you want to get kills at an equal risk of more deaths, use some of these.

GOOD:

SMITE:
-Required for jungling. You go too slow to be a viable jungler without it.
-Helps with tricky dragon/baron teamfights and protects your buffs.

IGNITE:
Since the dps is somewhat low on this build, and we don't need slows or escapes particularly badly, this can be useful. It helps a TON with finishing people off in mid-late game, as well as boosting your early ganks.

TELEPORT:
Teleport to tower/ward near teamfight, ult in, profit.
Save your feeding lanes and pick up kills!
I love so much about this spell, but you should pick an alternate if you know your map awareness stinks.

CLAIRVOYANCE:
This is viable purely because of the synergy with Paranoia. You know how sometimes enemies get away and you can't see them to ult at them? Fix't.

BAD:

EXHAUST:
Redundant on a frozen mallet/tank build.

GHOST:
Highly diminished returns during Duskbringer, plus will normally be slowing your targets.

FLASH:
Pointless on a tank with no area damage.

DUSKBRINGER:
-Fairly strong offensive spell.
-Hard to hit on champions.
-Difficult to aim in teamfights.
-VERY powerful mobility, worth using even if there was no damage.
-Helps with jungle speed in early game
-I chose to max with this skill first, mostly for farming boost.
-Diminishing returns on movespeed already take effect at rank 1 of this skill, with the soft cap beginning to take effect at rank 3 if you have Force of Nature or Nimbleness .

SHROUD OF DARKNESS:
-Extremely strong at rank 1, weak rankups unless you are stacking AD.
-Mostly used for blocking CC on yourself during ganks, but also nice during teamfights/other scenarios.
-I did experiment with ranking for more spell shields, but a lot of them were wasted and useless.

UNSPEAKABLE HORROR:
-The damage itself is slightly less than if you ranked up duskbringer, but this has a 100% hit chance.
-On top of being comparable dps, ranks allow you to add even MORE control to your slowing/tanky build.
-We max this second for the control synergy.

PARANOIA:
-While it's up, your enemies can't even see their pets or clairvoyance. It over-rides Twisted Fate's ult.
-While of itself not very damaging, it can completely wreck any chance of coordination the enemy team may have had.
-This particular build uses it for teamfight initiation, and quite effectively.

Overall: We start with Shroud of Darkness, get Unspeakable Horror to rank 1 at 4, and then max out Duskbringer first.

This is going to be fairly concise for now, if someone requests it I can add a mathcrafting section later.

Beginning:
+ -> + x2-> + x2->
This is the strongest start I've found through experimentation. The early jungle is extremely fast because of the Long Sword, and having runes/masteries to keep you up.

Balanced path, use against most teams:
-> -> -> -> -> -> -> -> -> -> ->
Standard build for somewhat split damage teams. Ordinarily, mages will avoid blowing burst on you, but physical carries shouldn't be afraid to chop you for a while, so it's slightly more armor heavy. The second Warmog's Armor replaces Wriggle's Lantern; Phantom Dancer replaces Ninja Tabi.

Armor path, use against teams with max two tanks with magic abilities (or one assassin):
-> -> -> -> -> -> -> -> ->
This path is designed to maximize your uptime and damage against physical enemies. The second Warmog's Armor replaces Wriggle's Lantern. This will work equally well for killing full physical damaging tanky teams if you pick up Madred's Bloodrazor instead of the second Warmog's Armor.

Magic Defense path:
-> ->etc.
Same as Balanced path, but with mercury treads and (if possible) back-booked magic defense runes.

1. Take Shroud of Darkness for your first skill point, and a Long Sword+ Health Potion. Go to mini-golems first. Open with a simultaneous Smite+ Umbra Blades. Pop your Health Potion. You should hit level 2 and pick Duskbringer.

2. Go to wraiths. Hit all three red wraiths with Duskbringer, then hit all 3 with Umbra Blades and kill each of them individually.

3. Go to wolves. Open with a Duskbringer from the side so you hit all of the wolves, then kill the Orange wolf first. Use Duskbringer twice, trying to hit all 3. If you have at least 200 health remaining at this point, go to Blue and kill the small lizards (save Smite). Recall and buy a cloth armor and 1-2 Health Potions.

4. Go kill blue, use smite when he is at 495 or less health. Use Duskbringer every time it's up, aiming for the chunk of wall so as to not give yourself away through the wall with the shadow trail.

5. Go kill the small lizards at red buff and mini-golems (or just golems). From here on your jungle is open-ended, but I would suggest getting Madred's Razors and two Health Potions before attempting red.

6. Gank whenever jungle is mostly clear and you have red buff (or a number advantage).

7. Ward dragon constantly with Wriggle's Lantern.

-When ganking, try to let your partners be in position to help (when you need it or they are close by)
-In teamfights, always be the initiator. Play smart about whether or not to use your ult for this.
-WARD WHEN IT'S NEEDED!
-Be a team player, don't rage at your partners when they do bad, help them!
-Don't argue with people if they try to start a fight, just say nothing and let it go.
-Tell your team that you intend to tank before the match starts. Also request they do not pick a second tank. People will assume you are dps Nocturne, if you say nothing.

-Sometimes it's better to use Duskbringer at the bush during ganks, rather than at your target. That way you get ahead of them.
-Try not to go for harder ganks without Frozen Mallet or red buff.
-When in doubt, move back. (AKA use common sense before you dive)
-Don't be afraid to finish people off with your ult/dive towers if you know you can get them safely.
-Wipe out lane waves with Duskbringer+ Umbra Blades
-Practice your spell shield, it is your most powerful move once you master it.