They'll never know what hit'em (or rather what WILL hit them).
When I first started playing MTG, this was my dream deck. After many years of playing and collecting I just recently assembled all the parts necessary to build it.
The main theme is maximizing the use of the Ninjutsu ability to wreck as much havoc as possible.
The main set-up creatures are Augury Owl and Dimir Infiltrator, the first one being an amazing 2-drop that not only has flying to start the party early with the ninja, but also has an extraordinarily deck-fixing Scry 3 for no additional charge. Dimir Infiltrator, being an unblockable 1/3 creature provides another entry point for the ninja and is a decent early game blocker if need be; but in case it has overstayed its welcome it can be traded for something more useful thanks to its Transmute ability.
Once the set-up is ready, the party can really start with an variety of ninja creatures. Ninja of the Deep Hours is the main grunt, delivering a decent 2 damage a pop and giving you enough drawing power to not worry about not having enough answers to your opponent's actions in your hand. Combined with Augury Owl, it basically guarantees that you will draw what you want to draw when you want to draw it.
Playing a supporting role are Mistblade Shinobi, clearing any threats too big to block, setting them up to be countered; and Walker of Secret Ways, always ready to evacuate any ninja that may be endangered at the time.
Finally the big honchos are Higure, the Still Wind, who will make sure that the right ninja are not blocked while he can also bring more people to the party; and Ink-Eyes, Servant of Oni, a powerhouse ninja that can regenerate herself and also steal any valuable dead creature to use your enemies' strengths against themselves. Also, as a reliable third string you have Mirko Vosk, Mind Drinker, a vampire that can be used as either yet another ninja enabler or in its own right as a punishing miller.
To provide cover to your ninja, there is an array of counterspells and removal options, as well as Whispersilk Cloak to keep your ninja out of reach from removal spells. As an added bonus, you can power up your unblocked attacker with Quietus Spike to bring the pain to your opponent in case they are running a life draining strategy, and Hero's Blade to buff up your legendary ninja the moment they hit the ground.
On the bench, we have Kozilek's Shrieker and Benthic Inflitrator to deal with any pesky protection spells. Oblivion Strike is there as well to substitute for any removal spells that may be affected by the same issues or to deal with indestructible creatures. In case you are facing a deck with black creatures, I added Walk the Plank as an alternative, although other options are available , such as Dark Betrayal, Murder or Go for the Throat.
For crowd control, I chose Icy Blast, since it can be used to deal with large numbers of creatures at a relatively low cost without blasting your own creatures and, with the right ninja on the field, it can also lead to a counterstrike once those creatures remain tapped. To deal with continued token producers that manage to elude the removal spells or creatures that keep coming back from the grave, we have Throat Slitter as a continuing creature killer that doesn't need to interact.
Finally, Okiba-Gang Shinobi is there in case you wish to keep an edge on card advantage against a control deck, though Millstone could take its place in case you want to take a milling approach using Mirko Vosk, Mind Drinker as the focal point of the deck.
