Who do you think the Hero's Shade is? Why do you think his spirit lingers on?

This is why I want a 3rd final Hero of Time game where we play as a true naturally aged adult Link who’s an actual adult. 17 is not an adult, it’s a teenager.

"Go and do not falter, my child" is also what the Great Deku Tree tells the Hero of Time as he sends him on his quest towards Hyrule castle.
Making it more fitting to me that he is using the same words he was told so long ago to the new Hero.

Another fun detail in the mannerisms of the hero's shade is that while he is Z targeting us during training, he does the same sort of shuffle with his feet that only the hero of time does. It's a detail I love.

Not being able to pass on his knowledge is definitely a more noble regret than not being remembered as a hero. It also could imply he died in battle (cause armour post-mortem is a common trope for undead characters), possibly right around his child being born and therefore being unable to raise them/teach them what he learned.

I think Link marrying Malon makes sense not only because of TP Link's start on a ranch, but also due to her presence in the game: Malon's voice can be heard singing in Hyrule Fields at night.
The reason we can still hear Malon could be that she is waiting for Link to complete his unfinished business (training his decsendant) so that they can pass on together.

OoT Link marrying Malon makes the most sense since TP Link lives in a farm village

The red eye can be explained by the Lens of Truth, which corrupts the eye of the person who used it. We see this in Bongo Bongo,  the Sheikah who owned the lens, became obsessed with it and turned into a horrific creature with one red eye.

The "curse of the swordsman" is an obsession with the lens.

the hero’s shade is genuinely one of my favorite parts of zelda lore

I think the fact that he possesses the Master Sword's scabbard, but not the sword itself, is meant to be symbolic of the fact that he never got to pass on the mantle. The sword is stuck in a pedastal, but the scabbard, the tool of the person who wields the sword, remains with him, because he could never pass it on to someone else.

As far as what happened to the Hero of Time after Majora's Mask, I generally infer that Link returned to Hyrule after that game. The big lesson the Skull Kid had to learn was that the Four Giants were still his friend even after they had left, and I think the ending implies that Link took this lesson to heart and ended his search for Navi, choosing instead to return to Hyrule, content that Navi is still his friend.

Looking at his armor, I always assumed Link joined the royal guard and enjoyed a distinguished but otherwise mundane career. Forget peaking in highschool, the peak of his life effectively didn't happen. That would screw with anyone.

And now a hero’s purpose by majorlink is describing this perfectly

Actually, I think the reason why OoT/MM Link sings the Song of Healing first is because he thinks TP Link has been affected by a curse that turned him into a Wolf and is trying to return him to normal.

The fact that the Hero's Shade says his regret is not being remembered. It makes sense. The child timeline Link left no memory in that timeline of his feats as the Hero of Time. Though he never forgot, the world he lived in never knew those feats. All his skills and experience would've had to be downplayed throughout his life as, whatever life he lived, likely could not have given him the level of experience and skill he gained fighting alone against Ganondorf's reign. Which meant, he could not pass on those skills and knowledge until TP Link.

I do like the idea of him returning home to Kokiri forest to rest and it being where he awakens years later to guide guide his descendant

“In the end, the Boy from the Forest returned home”. Amazing way to end the video!

And while the mangas are not considered "Canon" by nature.
The TP manga adaptation not only outright confirms that Shade is OoT Link, but also makes TP Zelda Remember her past life as OoT Zelda and embrace his memory and existence, welcome him back. Its beautiful.

2:05 I am really surprised that this attack here is animated correctly. When you strike with the sword, you need to also move the shield forward to protect your hand. So many pieces of media get this wrong, so I am surprised to see the correct movements applied here.

I think it's poetically tragic that HoT spends Majora's Mask soothing the troubles of others, living and dead alike, only for he himself to become a haunted soul in need of healing. It's a real balm that the Hero of Twilight, after centuries, gets to be for the Hero of Time what he himself was for so many others. I really hope that, one day, unseen by players, he did find Navi at least. Boy deserves that much.

Also with the mention of the first song you howl together with him being the Song of Healing, I really have always liked the theory that this is an attempt by the Hero of Time to cure Twilight's wolf transformation.