His Weapons

Katanas:

Homura

Sora

These katanas were gifted to Subaru as a gift from his parents after he completed his firebending and airbending training. His father forged the blades himself as he was pretty good with the craft. He duel wields the katanas whenever he isn't using his bending. And just like Aang was able to use his airbending with his air staff, Subaru can use his firebending and airbending with his katanas. He even gave both of them the name Homura and Sora, meaning fire and air.

Airbending Staff:

Subaru's airbending staff was a gift from his mother after he completed his airbending training. The airbending staff is a wooden stave used primarily by airbenders to augment their bending. These versatile instruments were a major part of Air Nomad culture and used in the execution of several complex airbending techniques. Staffs were constructed to unfold into fan-like gliders, which enabled airbenders to fly while manipulating the air currents around them.

Energybending:

Energybending is the ability to bend another person's life energy. It predates the four main bending arts, the formation of the four nations, as well as the creation of the Avatar. The capabilities of energybending are not well understood; what is known is that bending a person's life energy can impart them with knowledge instantly, remove their bending completely, or restore it. This bending art can be perilous to the user,[1] which is why so few have ever used it. In addition, even though mastering the four elements is a necessity for the Avatar, learning energybending is optional.

Subaru learned how to do this during the sanctuary incident, where he was lost and didn't know what to do, he ended up calling Avatar Korra's spirit and she later on shared the knowledge of energybending onto Subaru. I think you can imagine what'll happen to Roswaal later on right?

(It was going to be Aang or Genji originally but I chose Korra cause why not.)

Avatar Spirit:

As the Avatar, Subaru is able to contact his past lives to seek advice and guidance. Being the immediate predecessors of Subaru, Korra or Genji most often came to the young airbender's aid. Sometimes other past Avatar's came to his aid, like when Lye ended up devouring Subaru's memories, which ended up being his undoing. As without Subaru being able to control the body, the avatar spirit, to which he has a deep connection to due to being the avatar, one of the predecessors to take over. The one who is arguably the most powerful. The connection was able to be fixed due to a side effect of Lue eating Subaru' name. Which forced the avatar spirit to the surface as a means to defend itself.

The Avatar State:

The strongest and most powerful ability that the Avatar can invoke is the Avatar State. This state was created when Wan permanently bonded with Raava by touching the energy coming through the spirit portal during the Harmonic Convergence in 9,829 BG. It allows the Avatar to channel vast cosmic energies and the knowledge of previous Avatars, granting them increased strength and the ability to perform especially powerful and extraordinary feats of bending. The Avatar may unconsciously enter the State in response to the perception of mortal danger or high emotional stress, utilizing the State as a defense mechanism. While in this state, the Avatar has access to bending techniques that may have not yet been learned in their current lifetime but typically has no conscious control over the resulting actions if the state is triggered reflexively or momentarily, which can cause great collateral damage. An Avatar with full mastery of the Avatar State has conscious control over the State and can enter and exit it at will.

Shadow/Yinbending: Shadowbending is ability to control darkness and shadows. Subaru managed to create this form of bending from seeing demonstrations of Beatrice using shamak and minya multiple times. Darkness is the element of control, consisting of sneak attacks and overwhelming darkness tempered by the unflinching will to conquer. Shadowbending draws its power from the lack of light. The technique is notable for its manipulative battle style and usage. Subaru is able to manipulate the shadows of others, manipulating darkness, etc. And by using air bending/fire bending or water bending motions, he's able to expand on the moves, like creating gust of fog or icicles or even blades of shadows with a fiery appearance that upon contact, can do the same effects that yin spells would have. The kind of moves Subaru can use with shadow bending is more or less making a shadow whip, a shadow fist,  a shadow circle, etc.

Subaru completely masters this craft by the end of arc 4 and going into arc 5.

And that's all. See ya'll later.