Power & Abilities
Saimyōshō
Naraku's minion wasps from hell. 

Saimyosho
Added by Sesshomaru2010
They are useful for stopping Miroku's Wind Tunnel, spying on his enemies, and gathering Jewel shards. Their stings are fatally toxic to both humans and demons alike, but they are rather weak as demons come and are thus easily and numerously slain by InuYasha's group.
Shapeshifting
He can take the form of anything he chooses (usually a humanoid), and change his voice along with his physical appearance. He can also change his body however he wants. This is seen when he fights Sesshomaru in an attempt to absorb him and when he fights Moryomaru to reclaim Akago.  
Demon puppets
Puppets which resemble him. He controls them from afar and can see through their eyes. They are mostly made of mud and soil, and are able to spring roots in order to attack opponents.
Superhuman strength and speed
Much like Sesshomaru, Naraku is far stronger than a normal demon and can move faster than the eye can see, both in the air and on the ground.
Flight
Similarly to Sesshomaru, Naraku possesses the ability to float midair, and to ride upon a cloud of his own shoki. After his transformation into a full yokai, Naraku never chose to employ his shoki-sustained flight, but flew only by the strength of his will.
Demon parts
As he is made up of multiple demons in one body, Naraku is able to manipulate their body parts at will in order to restructure and strengthen his body, and he can also regenerate himself from injury and reform his body parts if they are cut off. He most commonly uses these parts to form tentacles which he uses to attack.
Absorption
Naraku is able to absorb other demons into his body, adding their powers and body to his own. This is primarily how he gains strength, by seeking out and absorbing strong demons, giving him access to their powers. Naraku can also expel weaker body parts in order to rid himself of them.
Psionics
Naraku has shown using various psychic powers and capabilities; including levitation, telepathy, telekinesis, teleportation, mind control, illusion-casting, and astral projection.
Detachments
He can make incarnations out of his own body to do his dirty work for him. Most have a spider mark on their back which is a result of being born of Naraku when he still was a han'yō with Onigumo inside him. After he purged himself of his human presence in the countless lumps of flesh inside Mount Hakurei, he and all his future children were free of having that scar on them.
Barrier
A barrier which prevents the foe from finding and/or attacking him. At first his barrier was only useful in hiding his presence. As he persevered in absorbing new, stronger demons into his body and discarding the weaker ones, it became powerful enough to survive the Kaze no Kizu, which is why Inuyasha needed to obtain blood from the bat demon, Taigokumeru, in order to penetrate. After Naraku became a full demon (in a sense) the barrier became so powerful that nothing but the Kongōsōha was able to pierce it.
Demon Control
Whenever someone sends an attack of yōki (demon energy) into Naraku's barrier he can channel the flow of the attack into his own jaki (yōki aura) and then attack his opponents with it. However, this can only be done with attacks that cannot penetrate his barrier, which means it's useless against Inuyasha's Kongōsōha.
Regeneration
Naraku can quickly heal his own wounds and also put back together severed pieces of his body. He can control 100% of his body all the time (even when severed), which comes in handy when he is trying to absorb someone. However, there is a limit to how much he can regenerate. The more damage he takes, the more time he will need later on to recover. Too much damage can kill him, which is why he had to flee from his enemies in the beginning of the series. Usually, he will absorb demons to speed up his regeneration process. However, after he removes his heart, which comes out as Akago, he was able to regenerate no matter how much damage his body took since his life force wasn't in his body.
Human/Demon shift
Unlike Inuyasha, who is forced to become fully human on the first night of a new moon every month, Naraku, as a half-demon with Onigumo inside him, could choose what time of the month he lost all of his powers and became human, although he was merely a human head attached to a mass of yokai parts during this time, which he used to experiment with his body and rid himself of any unnecessary parts. Since the events that have transpired on Mt. Hakurei, he no longer has to become human at any time, being a full-fledged yokai.
Beam attack
Naraku sends out one or more of the horns on his elbows in a zigzag beam attack or extends his fingers into tentacles with a glowing attack at the tip of fingers to attack his foe(s). In the manga this attack was of a silverfish color and in the anime it is of a purple color. Furthermore, even though this attack is a yōki attack, because Naraku is using his body parts infused with shōki to attack his opponents, Inuyasha cannot use his Bakuryūha (Backlash Wave) against it since it counts as a physical attack.
Miasma
Naraku's trademark, a poison which kills anything that touches it. It's what makes his poisonous gas. Naraku uses it to cover his entrances and exits, and can surround himself with the gas while flying. He created a "false Shikon shard" for Kōga with this substance. It was able to power Kōga in the manga and anime for a while until it backfired, poisoning him, and ultimately leading him to remove it with the help of Kagome. Naraku's body is filled with it, which is why when a foe bites him or even touches him he/she gets poisoned. Later on, as his power grew upon his transition to full demon, his shōki is able to take on a liquid form and acts like a river of acid. His shōki is so strong that it allows him to break away pieces of the nearly completed Shikon no Tama to use in his schemes. In the current manga, he can melt entire mountains. Over time his shōki has become so dangerous that after he infects Kikyō with it, neither Kagome nor Kikyo's holy powers seem to be able to purify it. Kikyo absorbs Midoriko's soul in order to protect herself but she comments that she doesn't know how long Midoriko's power can last against Naraku's venom, in the regard that she and Midoriko remain at the same strength while Naraku continues to increase in power. Eventually, even the influence of Midoriko is nullified with Naraku's absorption of the tree and Mōryōmaru.
Live Body Pieces
After absorbing Akago/Mōryōmaru, Naraku gained the power to merge pieces of his body with other demons, thus giving him control over them and increasing their regenerative abilities. He can send pieces of his body abroad to scout for new demons, for him to add into his body. It is important to note that these pieces, after becoming separate of Naraku's body, became living beings that can move and fight on their own.
Shikigami
This power is only displayed in the Playstation 2 RPG InuYasha game; InuYasha: Secret of the Cursed Mask. He obtained this power by deceiving Utsugi, a 'hitogata' (clay doll demon) duplicate of the original Utsugi, who was created by the priest Kakuju to ease his/her suffering when his/her real wife/husband died. Utsugi (the hitogata) required the soul of a relative of the real Utsugi, and a large portion of the Shikon Jewel, which Naraku provided, and helped in retrieving shards from Koga to become a true, live human. When Naraku supposedly died (w/ jewel on hand) at the hands of Inuyasha & co, the leftover jewel was retrieved by Utsugi behind the scenes. When Utsugi finally retrieved the soul she/he needed (which as it turns out, was Kakuju's) Naraku's voice began echoing from the Sacred Jewel, and Naraku took over Utsugi's body rather than absorbing her/him to acquire her shikigami-channeling powers. He became able to use the destructive power of an unknown variety of shikigami, and would time-to-time spout out a long verse when he attacked during the fight in the game. Because this only happens in a game based on the anime (which wasn't entirely canon from the start) and the events of the game stray away from the actual cliffhanger ending of the anime, this power is un-canon.
Phantom Castle
Naraku is seen having the ability to create various "Phantom Castles" as a temporary headquarters throughout the series.
Dormancy
Naraku has the ability to hide himself within one of his servants and make it appear as though he has disappeared, or have been killed, rather. A simple task; he gets himself "killed'" and hides within the body of a servant of his choice.One of the first times we see this is in the second movie when he hides in Kohaku's back he seems toleave a spider mark like his on who ever he lays dormant in. To reinforce this fact, he even (although temporarily) removes Miroku's Wind Tunnel and returns Kagura's heart.
Black Magic
Naraku knows many different spells and curses, a prime example being the Wind Tunnel.
Armor Shell
Upon absorbing Mōryōmaru, he gained the ability to cover himself at will with Mōryōmaru's impenetrable shell. It has been revealed that Naraku is hiding the Shikon Jewel underneath this shell.