OVERVIEW
Carry is N'kari's only viable role. His early game is too weak to survive any other lane. But if he can hold out his late game becomes brutal. For his skill build Sadomasochism should almost always be maxed first as it's his farming and laning spell. Witstealer sword is typically leveled last as it doesn't benefit farming and is most useful later in the game as a dueling tool, a single point is typically good enough for the early portions of the game anyways. For his talents getting all Sadomasochism talents is ideal if you're winning the game as it becomes incredibly power with all talents. If the game isn't going so good though then his other talents can allow him to play more around pick offs and catching key targets.
In the early game build what you need to survive most of all. A vanguard gives you some valuable HP and damage block which is really good with Sadomasochism, it also builds into Abyssal later. Scepter is N'Kari's farming item. The build up might be bit rough, but in the end it's cheaper and stronger late game than Battlefury and it synergizes with illusion. Speaking of illusions, manta style is your big core item. His illusions benefit from both his passives, the scepter, and the shard, making his manta illusions scale like beasts. Skadi of course goes great with illusions and give you some of that beef and mana you're missing. Shadow blade will give you the mobility and pick off potential and combined with Willing Prey it's like you already heave an Orchid. Butterfly, Abyssal, and Moonshard are the late game finisher items for N'Kari.
For situational items BKB might be required against high magic damage line up. Swift blink for when shadow blade just isn't fast enough. Crit is great with your scepter and illusions, so good that you might want to buy Daedalus in addition to your shard for crit chance, especially if you got a blink instead of a silver edge. Heart for if you really don't want to get bursted anymore. MKB when evasion is a factor. If you're stinking rich getting a radiance instead of a scepter early and then going back for the Aghs Blessing can get you even more farmed than before.