For avatar Yin, the past 10 years were an opportunity to discover himself, he worked mostly on balancing his emotions, and retrieving his connection with his past lives, which he still wasn't able to do.
He visited the secret library in the spirit world, and offered his knowledge of the new art that is glassbending as an exchange for a ton of knowledge concerning emotions, he even became a hikikomori for 3 months.
He also worked on glassbending, and created the glassbending scrolls, which were unique compared to other bending scrolls; any bending scroll always shows a person performing a move, but glassbending scrolls show 2 people in each move, because glassbenders don't fight, they reflect the enemy's energy onto them, there are a few single moves, but those are used for the basic training, actual fighting moves always require an enemy.
The way he trained glassbenders was a lot like how airbenders train, avatar Yin admired how calm and wise airbenders were even during the hardest times, their training lasted 2 year, 1 year of spiritual training and 1 of physical training, then they built their city in 4 years, and were only allowed in a year later after the secret places the avatar and some trusted benders were built.
Unfortunately, since Yin still hasn't mastered firebending, and even some hard airbending tactics, he is still not able to access the avatar state when wanted, Raava asked him not to;
Yin was at the western air temple meditating, when Raava suddenly came out and put herself in front of him, he was surprised to see her, and before he could ask her anything, she spoke up
"I know you're planning on starting your avatar state mastering soon, but I insist on not doing it. The element jewelry affect someone if they're merged with him, that's why anger was one of the main emotions you felt while having the fire ring, and now you will do some stubborn acts because of the earth necklace, plus they add a lot of power to you, and your spirit and body need time to adapt to it, also, the main thing; if I or Vaatu get destroyed, every 100 years, we will start to grow a bit inside each other, and Vaatu's first 100 years are very close, I'm afraid the powers you would produce while training will benefit him, do not start your avatar state training until you are able to fully control your powers and emotions" and with that she went back inside of him, leaving him sad because he wouldn't be able to walk on that powerful purple path and fully merge with his internal consciousness and avatar spirit, like all avatars past him did.
Yet he knew that's what he should do, so he held himself back from starting his training.
The only danger that happened in the past 10 years was Yin's visit to the Wan Shi Tong's library, more known as the big owl spirit.
When Yin reached it, he airbended himself up, the library was still where avatar korra left it, way above the ground, hung between 2 trees. When he first came, he was immediately hit by Wan Chi Tong, and slammed to one of the shelves, his wolves stood in front of the books protecting them, and some came to attack Yin
"Please, I just came to read some books" wailed the avatar as he ran from the wolves
"Avatar Aang betrayed me, and my experience with avatar korra wasn't good either, get OUT OF MY LIBRARY" howled the owl in annoyance.
"Sorry for what I'm about to do" thought Yin to himself as he jumped to the middle of the library and created and air tornado that sucked everyone in, then he earthbended and stuck them all to the walls. After that, he flew to the owl and glassbended one of the windows, and he played with the shape of the glass, then ge said "that's my new piece of information, glassbending is doable, it's an extension of sandbending, which is an extension of earthbending. But I feel bad if I'm going to keep you this way, I'm freeing you but please, don't hurt me, I'm meaning no harm, I promise" he backed up and let them all free, the owl got up properly and just starred at him, not saying anything. Yin took it as an ok, and went on with his search.
Other than that, the past years have been peaceful, at least that's what everyone thought.
After studying and meditating a lot, Yin finally designed the 10 glassbending scrolls; training I, II and III. The 7 other scrolls were divided this way: one as a defense from firebending moves, one from earthbending moves, one from airbending moves, one from waterbending moves, 2 from martial arts' moves, and one for attacks.
He also wrote a book about spiritual training, meditation positions, the inspirations for many glassbending moves, the intersections between the four bendings and glassbending, and the intersections between material and physical trainings. All glassbenders were obliged to learn the 3 training scroll, the other scrolls were not a requirement for citizens to learn, but it was for the guards, each one needed to know at least 4 moves of each scroll and whoever wanted to master the bending art needed to learn all scrolls. He even created a secret bending move that only he knows about, titled "the scorpion sting" which was able to quickly end any life, which is why he kept it hidden, and promised himself to only use it when it's his last hope
The scorpion sting is a move where Yin would shape the glass as a scorpion's sting, and at the end of the tail lies 1000 tiny glass spikes, the tail would stick to his back and its end would be above his head, just like how the scorpion moves his tail back then forward to sting, the avatar would do that to shoot the spikes and help them become faster by glassbending, because of how sharp and small they are, they would dig someone's skin very quick and penetrate their body, then the avatar could either make the spikes come out or use them inside the enemy's body to block their veins/ poke their organs to end them. Avatar Yin studied animals for about a month to make his signature move, and he settled on scorpions.
The only thing Yin still hasn't found the courage to do yet is visit master ushi again.