It's not fair that only the Three Stooges in Demon Slayer get the majority of the character and power development. Nezuko, after all, was a major character before even Zenitsu and Inosuke entered the picture. Thankfully, the latest episodes of the Entertainment District Arc have shown how much Nezuko has improved alongside Tanjiro, and it was jaw-dropping.
Up until that point, Nezuko hasn't flexed her full might. Now that she did and is about to even more (based on the manga), she's only going to get even stronger. Such are the perks of getting a blood pack from Muzan himself. Now, Nezuko has demonstrated the majority of her powers and techniques in the anime. This is what she's capable of so far.
8 Size Alteration
Nezuko's first exhibition of her demonic capabilities was already impressive. She was able to alter her body size and age, basically a limited shapeshifting. During her first scuffle with Tanjiro as a demon, Nezuko managed to grow her muscles and skeletal frame— enough to overpower Tanjiro, who's older than her.
When she's not jacking herself up with demon protein, Nezuko appears to be conserving her strength and form by maintaining a much younger and even childlike appearance. This also serves another purpose, which is to help Tanjiro carry her easier. Other times, she uses her size-shifting to evade attacks.
7 Hand-to-hand Combat Proficiency
Despite not having any combat training the same way Demon Slayers did, Nezuko can certainly hold her own in a fight. In fact, she's proven recently (at the time of writing) that she can even surpass Tanjiro when it comes to fighting Upper Moon-level demons. It's worth noting that she was on her way to defeating Daki or Upper Moon 6.
What's even more impressive is that Nezuko is a one-trick pony when it comes to combat where she mostly resorts to kicking her opponents. Even before the Entertainment District Arc, she was able to kick a demon's head clean off. It does seem that she has honed her kicking skills to perfection as she managed to do the same to Daki, obliterating half her head with a surprise kick.
6 Demonic Strength, Speed, & Durability
Of course, it does help that Nezuko's strength and speed are so inhuman that the Hashira were right to fear her. As stated before, Nezuko was able to overpower someone like Daki. While she was likely the weakest among the Upper Moon or Upper Rank demons, Nezuko managed to humiliate Daki, meaning it's safe to assume that she can take on someone like Daki's brother or even Akaza.
In combination with her demonic strength, Nezuko uses her speed to assault Daki from behind after feigning a full-frontal charge. Moreover, she was able to withstand Daki's attacks and even prevented some of her lethal sash swipes from fully dismembering some limbs. Prior to the fight with Daki, Nezuko was also able to go toe-to-toe with Susamaru and even win against a mock football fight with her.
5 Hibernation & Self-sustenance
Whatever Muzan's intentions were for transforming Nezuko into a demon, it seems his little experiment was paying off. Nezuko soon set herself apart from other demons by becoming semi-independent from the blood of humans as her sustenance. While other demons would have died of hunger, Nezuko only became weak when deprived of human blood.
As an alternative, Nezuko was able to hibernate for prolonged periods in order to regain her strength and demon capabilities without the need for human blood. This also explains why she's mostly absent during some of Tanjiro's smaller fights. Nezuko doesn't have the same stamina as other demons and will likely gas herself out if she fought with only hibernation as her primary diet.
4 Awakened Form
Most other Nezuko techniques prior to this simply paled in comparison. This appears to be Nezuko's true form if she gets rid of the bamboo talisman that's corking her powers. It's also Nezuko's most visually spectacular technique or ability as she grows into a mature form here with leaf tattoos and a horn on her forehead. Every demon power she has is also enhanced in this form.
Based on that alone, it appears it's not even her final transformation yet. There were some drawbacks to this technique as it necessitated an immediate or available source or storage of human blood which was why Nezuko tried to attack civilians. Additionally, she enters a berserk state or trance during this Awakened Form, making her a loose cannon.
3 Rapid Regeneration
After unleashing her Awakened Form or true form, Nezuko also gained regeneration to rival that of an Upper Moon demon's which is a testament to the strength of Muzan's blood. With this technique, Nezuko is able to instantly regrow severed limbs and even heal some lethal wounds.
She was even able to reattach her own severed head in the blink of an eye which is even more impressive as no other Upper Rank was able to perform such a feat yet in the anime. Daki herself was surprised at Nezuko's immense regeneration. Before this, Nezuko's regeneration was rather slow and she even needed help from Lady Tamayo after sustaining an injury from another demon.
2 Blood Control
What did help in keeping her immortal in her Awakened Form was her blood which was somewhat prehensile as she was able to control it like it was some kind of muscle or limb. Apparently, Nezuko can coagulate her exposed blood in order to control it better, practically turning it into solid once it's out of her body and presumably turning it into liquid again.
With this kind of technique, Nezuko was able to prevent her severed head and limbs from falling to the ground and completely detaching themselves from her body. Afterward, it was a matter of pulling her limbs and head back to reattach them. This makes Nezuko look even more durable compared to Upper Moon demons.
1 Exploding Blood/Pyrokinesis Blood Demon Art
By far, this is Nezuko's most damaging technique when it comes to fighting her own kind. Her blood contains special properties that make it deadly upon contact with other demons as Nezuko can immediately ignite her own blood in a pink fiery blaze as part of her blood control capabilities.
This is also Nezuko's first formal Blood Demon Art. In her case, it's Pyrokinesis as the pink fire blood has anti-demon properties and apart from causing some nasty burns to any demon in contact with it, it also prevents any form of demonic regeneration. Before her fight with Daki, Nezuko also used this Blood Demon Art to burn Rui's threads and even dispel Enmu's dream spell. Whatever Muzan gave Nezuko, it's well on its way to becoming a weapon against him.