Muktol

Personally I would play "Young Wolf" over "Wolfbitten Captive" because you don't have pay mana all the time if you want him big. And undying is a good mechanic that can drive your opponents crazy. I also run "Ghor-Clan Rampager" to buff a creature without having to actually cast a spell (it's an ability).
Sideboard "Naturalize" and run either "Ranger's Guile" or "Vines of Vastwood" as some protection is never wrong.
The mana base might be a problem but there are some (few) good and cheap ($)dual lands: "Rootbound Crag" and "Copperline Gorge"

Greetings
Muktol

If you want to use blue the obvious choice would be to built this as a control deck, with the combination mentioned by KJSJ3 as finisher.
But don't mix strategy's. Cards like "Military Intelligence" belong into a more aggressive built while "Vampire Nighthawk" or "Mana Leak" are more on the control/ mid-/ lategame side. The decision what and how to built this is up to you, but you'll have to make it and stick with it.

Greetings
Muktol

*like*
When using "Krenko, Mob Boss" I can suggest some cards, based on my own monoR Goblin deck (http://www.mtgvault.com/muktol/decks/monor-tribal-goblins/)
"Furystoke Giant", "Purphoros, God of the Forge"...two good finishers. The has instant board impact and can be used again thanks to persist, Purphoros is a killer in combination with Krenko
"Quest for the Goblin Lord"/ "Shared Animosity"...two buff enchantments. Quest is faster with only cmc1 but the Animosity can get stronger (tough you have to be careful as it counts for your AND your opponent's creatures)
"Mogg War Marshal"...basically a "Krenko's command" with a body
"Massive Raid"
"Legion Loyalist"...trample and first strike for all your attacking goblins. A little bit more unstable than "Bloodmark Mentor" but the trample can make the difference.

Greetings
Muktol

Some suggestions based on my own monoB sacrifice deck (http://www.mtgvault.com/muktol/decks/monob-sacrifice/)
"Sylvok Lifestaff"...can help you against decks that use burn or manage to threaten your lifepoints in any way. At last sideboard material.
"Blood Artist"...let's you convert dead creatures into damage and lifegain
"Undercity Informer"...let's you convert your deck from kill to mill. A card I really like , at last in the sideboard.
"Tragic Slip"...-1/-1 for cmc1. At last until something dies, then its -13/-13 for cmc1. No regeneration or indestructibility will use against this spell.
"Smallpox"...attacks all resources: Life, handcards, creatures and mana base. It's a little tricky to play because it targets all players, so the right moment is important.
"Blade of the Bloodchief"...you are not playing any vampires but a +1/+1 counter for every sacrificed/ dying creature (Yes, also your opponent ones)? Yes please!

Greetings
Muktol

"Phyresis" can handle that problem.
I would use creatures like "Consuming Aberration" or "Mortivore" or the enchantment creature "Nighthowler" as finisher to benefit from cards being put into your opponents library. "Runechanter's Pike" would be an option if you would use self-mill ore use a ton of spells.

Greetings
Muktol

When using high toughness creatures "Phenax, God of Deception" can be a real interesting card to mill with.
I also would cut "Traumatize" and "Mind Sculpt" and use "Mind Grind" instead. The only card you have in this deck that benefits from early mill is "Jace's Phantasm". Personally I would replace the Phantasm with "Kaijin of the Vanishing Touch". It's "just" a 0/3 defender but it forces your opponent to take his attacking creature back on his hand and cast it again.

A simple card to shut down Emrakul and other graveyard based decks would be "Yixlid Jailer"

Greetings
Muktol

I would rather use "Kiln Fiend" or "Chandra's Spitfire" than "Foundry Street Denizen".
Also a simple "Dangerous Wager" could prove rather useful since you will shoot your spells and get into topdeck modus.

Greetings
Muktol

Some suggestions based on my own monoR goblin deck (http://www.mtgvault.com/muktol/decks/monor-tribal-goblins/)
Try to get some "Goblin Bushwhacker" instead of "Goblin Piker". Same cmc (with kicker) but gives all your creatures +1/+0 for this turn.
I would try to change from "Curse of Stalked Prey" and "Trumpet Blast" to "Quest for the Goblin Lord". Normally a single, strong, attack is all you need to beat your opponent and the Quest is better here than the Curse and it's a permanent effect unlike Trumpet.
When using Krenko I would use "Mogg War Marshal" instead of "Mogg Flunkies". Gives you 2 tokens instead of 1 creature.
"Goblin Chieftain" is expensive ($) but he's worth the money. "Hellraiser Goblin" and/ or "Fervor" could be removed out for him.
"Leyline of Punishment" belongs into the sideboard.
"Battle Hymn" won't be of great use until you get some carddraw so I would rather use "Dangerous Wager" in it's place.

Greetings
Muktol

Some suggestions based on my own monoU mill deck (http://www.mtgvault.com/muktol/decks/monou-mill-2/)
I would remove "Traumatize" because it's just to expensive for what it can do. If you want to have an alternative take a look at "Sanity Grinding"
I also would remove "Curse of the Bloody Tome" in favor of "Hedron Crab". To make full use of the crab you could also trade some of your island for some searchlands like "Terramorphic Expanse".

Some other suggestions:
"Augur of Bolas", "Archaeomancer", "Visions of Beyond"

Greetings
Muktol

Just don't mess around with werewolf's as they like decks that don't cast spells (and ninjutsu is an ability and not a cast) ;)

That's clear to me and I hope to all other players also, so I didn't point it out.
Hexproof/ shroud is a rare gift among black/ white instant spells (in fact a quick search showed that there are none) so protection spells are a good way to achive this, even if you have to take care a little bit. Indestructible as well as regeneration would be an option. The advantage of color protection is that you can protect your creatures and give them evasion with a single spell. If you use spells like "Stave Off" then it's even possible to target your opponents creatures, negating spells your opponent want's to play on them.

In my opinion it's better to loose the enchantments (save "Umbra Mystic" is on the field then you should never use those spells to protect creatures from colors they are enchanted with) than to loose the creature and enchantment. There are enough enchantments in here to re-up some, but creatures? Not so much.

"Phyresis" can be very bad news for your opponent.
Also "Tragic Slip, one of the better point removals, could be interesting for this deck, especially if you don't manage to get "Umbra Mystic" on the field.
I would throw in some protection spells, at last in the sideboard, like "Brave the Elements" (or "Skeletal Grimace" if you want an aura) to protect my creatures.

Greetings
Muktol

I think "Trinisphere" will be crucial for such decks. 3 should be enough as you want to draw it but you don't need to draw it more than once.
"Detritivore" works good against decks that run many non-basics. When going against other decks I would favor "Magnivore". Personally I would use 1-3 "Magnivore" as finisher mainboard and 1-2 "Detritivore" in the sideboard.

I mean no offence but you might want to read
http://www.mtgvault.com/muktol/decks/how-to-build-a-deck/

Short version: Far to many cards (60 would be the optimum) and far to many different cards.

Greetings
Muktol

"Trinisphere", "Detritivore" and/ or "Magnivore" might be interesting for you.

Greetings
Muktol

Well they where a little faster (and better) before the 10th edition, when damage went over the stack. But nowadays...no they are definitely not the fastest guys, which means that one should pack enough control.

Perhaps you can take some ideas from my B/R vampire deck:
http://www.mtgvault.com/muktol/decks/rb-tribal-vampire/

Basically I would alter your creature list a little bit and add some carddraw. Some of those cards could also be put into your sideboard.
25 Land seem to be on the high side to me, I would try it with 20-22.

Greetings
Muktol

Some suggestions based on my own U/B ninja deck (http://www.mtgvault.com/muktol/decks/ub-tribal-ninjas/):
In would remove "Silent-Blade Oni" as it is the only card that ruins your modern legality.
Also "Nightveil Specter" isn't a good enabler (bring ninjas into the game with ninjutsu) because he's a little bit to expensive to play and he has no effect if you use him to bring ninjas into the game. "Tormented Soul" does the same job but costs less to play.
"Ronin Warclub" is a very interesting piece of equipment for Ninja decks as they normally lack the strength to deal real damage. You don't have to equip it because it equips itself to one of your creatures entering the battlefield...in an instant!
Spells like "Familiar's Ruse" or "Far // Away" might help you to play ninjas again with ninjutsu. Otherwise "Artful Dod" can help you to get them through to profit of their effect.

Greetings
Muktol

Some suggestions, based on my U/B standard mill deck (http://www.mtgvault.com/muktol/decks/ub-standard-mill/) and my U/B pauper mill deck (http://www.mtgvault.com/muktol/decks/ub-pauper-mill/):
Thought Scour, Pilfered Plans, Augur of Bolas, Drowner Initiate, Dream Twist

I would remove "Traumatize" because it's just to expensive (cmc) for what id can do. You could try "Increasing Confusion" as replacement
Also 24 Lands seem to be on the high side, you could try to lower the number by 2-4.

Greetings
Muktol

"Bile Blight" might be an interesting option for your sideboard.
"Read the Bones" perhaps as 2/2 split or instead of "Sign in Blood" (costs 1 mana more to play but the scry ability could increase your chance of drawing certain cards)
Otherwise it's looking good now. *like*