Ello again. I'm here to submit my case for why an indie character should be in Smash.
... yeah it's already a dead idea.
Still, I was able to compose a big list of design choices for the little tooth-headed protagonist. A lot of things from the game just translate really well into Smash, so I can totally envision the character well. I'm also going to post this on Reddit and see what the consensus is, cause I guess it'll get more reception there. Maybe we'll start a cult following, I dunno, it's more to work with then fricken sans.

Neutral attack
The knight swings their nail in a diagonal slash. Using the neutral attack again lets them swing a second slash, and if you wish, you could keep using the neutral slash one-two combo in place as much as you want, with the second hit having moderate enough knock back to knock the foe out of range. Then, as you stand there, trying to ward away your foe with your slashing, captain falcon finds the optimal time to jump in and super-knee you.

Side tilt
Side tilt is similar to neutral attacks, and I liken this to Mega Man’s side tilt, where he continually attacks while moving. This attack may or may not also knock the knight back a bit when they hit an opponent.

Up tilt
Their up tilt is pretty straight forward, an arcing sword swipe above them. Several knights may choose to play volley ball with Jigglypuff. They’ve practiced before.

Down tilt
The knight stabs at the opponent's feet. The animation of this attack is based on the animation when the knight reaches down and picks up something from the ground.

Dash attack
This attack is based on the dash slash, which produces a long arc in front of the knight. At least it did in Hollow Knight, for balancing purposes it was toned down quite a bit.

Neutral aerial
Instead of going for a cop out by just making the knight spin or whatever, this neutral air is based on either the spore shroom or defenders crest trinket. Both would produce a damaging cloud around the knight, either through spores or really bad smelling gas.

Side aerial
The knight swings their nail forward in midair, not much else to say.

Back aerial
The knight doesn’t really have a good candidate for this, whenever they turn around it’s like instant re-transmission or something. Therefore, we can take liberties with this and make the knight swing their nail back around them horizontally.

Down aerial
This is a more interesting move, which I would like reflecting how the knight functions in their game. The down air attack in Hollow Knight is like a pogo stick, it reflects the knight off whatever they make contact with. After this happens, the knight also regains their double jump once it is unlocked, and the combination of the two leads to some really interesting platforming. In a similar vein, if the knight manages to land a down air, maybe it won’t have meteor capabilities, but rather it grants the knight another double jump, making it a very safe gimp opportunity.

Up aerial
Basically the up tilt, but in the air.

Neutral special
The knight unleashes their soul energy as a vengeful spirit, a projectile that blasts anyone in their way. It should be properly lagged so the knight can’t simply spam it like they may choose to in other games.

Up special
This ability is the abyss shriek. In Hollow Knight it was a spell that blasted anything unfortunately above the knight, but for smash purposes, it also lifts the knight upward. This isn’t too farfetched either, the spell cancels the knight’s downward momentum in their game, and it has been used for platforming on occasions (as confirmed by the most insane speed run I’ve seen in a while). I’d like to see the abyss shriek over its basic form, howling wraiths, as it combines soul spirits with void spirits, which is a nice aesthetic duality compared to the neutral special and the down special-

Down special
-descending dark. The upgraded form of desolate dive also produces a shockwave when the knight lands, damaging anything right next to them or above them after the initial slam.

Side special
I entertained the idea of this attack being the sharp shadow dash for a while, and maybe that would also string off of the pogo jump I mentioned earlier, but I’m beginning to recall what happened when another certain... aerially gifted individual was added to smash in the past, so let’s not go that far that the knight can punish foes under the stage for free. Instead, the side special is based on the crystal heart, which once obtained allowed the knight to charge up a crystal dash, well it was more like a rocket than anything. It has some charge-up time, but when active can go as far as you want, and it will certainly do more damage than it did in Hollow Knight... just be sure to cancel it before flinging yourself off the stage. This is a rather risky move, either you make impact with the opponent, or you risk putting yourself in a vulnerable position. Stopping in midair is like an invitation for DK.

Side smash
This smash attack is based on the great slash, a nail art producing a wide arc in front of the knight. While charging smash attacks, the knight can be seen glowing white.

Down smash
This one is based on another nail art, the cyclone slash, which has the knight spin around.

Up smash
There isn’t any nail art for upward attacks like Roy’s up special or anything, so this up smash is based on the dream nail. Particularly, the dream gate animation. The knight, later in their game, can use the dream nail to produce a dream gate, then at suitable location they can charge their dream nail facing upward to teleport to the gate. This up smash won’t send the knight anywhere else, but will release a barrage of dream circles to damage the opponent.

Shield
One of the knight’s signature abilities is the focus, which allows them to channel soul energy to heal themselves. This would be broken, but fortunately a certain charm allows us to use the focus in a different way, create a baldur shell as a shield. I’m not saying that the shield in smash will look like the baldur shell, I’m just saying the focus animation can be used while the knight is holding up their shield.

Parry
The moment where the knight gets a perfect shield looks like the end of the focus animation, where the knight pulses with soul energy.

Forward dodge
This is where I include the shade dash, as the knight phases through any opponent in their way.

Back dodge
In early trailers it was shown that the developers of Hollow Knight gave the knight the ability to backstep away from enemies. This was taken out of the main game, but it still gives us material to work with.

Spot dodge
I’m really not sure about this one, I suppose it will be the same sideways dance move as most other fighters.

Grab
When grabbing the opponent, the knight reaches out one hand, based on the animation when obtaining something that isn’t on the ground. The knight doesn’t really grapple in their game though, so what happens from there is basically...

Pummel
The knight beats the grabbed enemy with the blunt of their nail.

Forward throw
The knight whacks the enemy in front of them, sending them off.

Up throw
A dinky upward toss.

Back throw
The opponent is tossed over the shoulder like the trash they are.

Down throw
The knight performs a triple horizontal spinning suplex on the opponent!!! AAAAAAHHHH HUNDOOOOOOOOOOOOOO! Just kidding, the down throw is a typical slam against the ground. Really, if anyone has better ideas for the throws, let me know. I was thinking how there could be creative liberties, like the knight’s shade leaving their body and tossing the opponent somewhere, but that seems a bit excessive.

Idle
The knight doesn’t really do much, and will stand firmly in place. Their nail is always sheathed when not in use, only being drawn to perform attacks, then sheathed again immediately after. Given enough time standing still, the knight may get tired and dip their head down a bit before getting a hold of themselves. Another idea is that the knight will pull out a map briefly to make sure they didn’t end up on the wrong side of Pac-Land.

Movement
The knight can walk, the knight can run, and the knight can even sprint given the proper resources in Hollow Knight. All of these animations can carry over to smash. In case you aren’t aware, few things are quite as adorable as a swimming knight. As a crouch, the knight will duck forward. You can actually move the knight’s head in Hollow Knight by pressing up and down or messing with the camera controls, so the crouch is just a more extreme way of looking at the floor.

Stage entry
The knight wakes up from its brief rest on a bench and gets up. The bench then quickly folds up and retreats into the ground.

Damage animations
They have a perfectly valid hit stun animation where they face more towards the camera while being knocked back. I swear, it’s like they designed them to be a smash character. And if they refuse to get up when they impact the ground after a particularly heavy blow, they just lay there before getting themselves back on their feet. Which also leads into the next categories...

Floor attack
If attacking while knocked down, the knight arcs the nail overhead. This is more in reference to the attacks of other similar entities from the game.

Rolls
They’re actually just rolls. Maybe the knight has to roll along sideways because of the big head, I dunno.

Ledge animation
The knight actually has a ledge animation, used in exactly one cutscene. If they hold on too long, they fall like that Lion King scene. They can hoist themselves up similarly to the animation from when they wake up on the ground, and the same applies with that down tilt animation I referenced.

Shield break animation
If at any time you throw the knight into a bunch of spikes or some abstractly placed sawblade, the knight does an animation where they are flung upwards before tumbling to their demise... and then respawning at a nearby safe ledge. This same animation can be replicated for having their shield broken by the enemy. The daze animation, look, every character has the same dizzy animation anyways.

Double jump
In Hollow Knight, the double jump is achieved by obtaining the monarch wings, allowing the knight to produce white butterfly... dragonfly? Bug wings to propel upwards. Seeing as I wanted an actually threatening up special and not just a trampoline, the wings are showcased any time the knight double jumps.

Wall jump
And what do you know, they have the ability to wall jump, just like their game, who would have thought?

Up taunt
As a show of challenge, the knight pulls out their nail in a battle stance.

Side taunt
The knight bows courteously to their opponent.

Down taunt
The knight plunges the dream nail into the ground, producing a dream gate, which immediately dissipates afterwards since there’s a time and place for everything, but not now.

Skin ideas
Now our stretch goal here is to get some actually unique skins here, maybe different head designs. By default, the knight’s head sports horns that kind of look like a broken hoop, but other skins could be different horn designs present in the game, four shorter horns, two pointing downward, and other designs we see present on the remains of the less fortunate in Hollow Knight. I’m sure one horn design in particular may be a fan favorite. Of course, if Sack wanted to go the route of simple recolors, well, all the knight has is their head and the cloak, but we could color them in a way akin to other characters, most notably a red cloak based on Hornet and then whatever color palettes we have that aren’t just more shades of blue-gray. A purple cloak and pink head to represent the Seer, a dark blue cloak and somewhat brighter blue head for Tiso, uh, a pink cloak and dark blue head for the Dung Defender? Just straight up white-knight? Black headed knight, like the shade? For the last skin, a knight that’s completely chrome, a reference to steel soul mode.

Final smash
When the knight unleashes their attack, void tendrils erupt from the ground in front of them, attempting to ensnare an opponent or two, or seven if you’re that insane. Any caught opponent is brought to the center of the stage as the knight’s shade breaks from their body, using more tendrils to strike the opponent multiple times, before unleashing one last finisher blow to knock the enemy away. Then the shade curls up and re-enters the main body.

Victory poses
Pose 1, the knight drops from above, with vengeflies flying out, and the screen pause occurring with that menacing blank-eyed muffin staring you down. Pose 2, the knight sparring with its own shade, and just as it delivers a finishing blow on its own shadow the screen pauses. Pose 3, the knight finds a bench and sits on it, it all comes full circle.

That's my own take on all of this anyways, let me know what you guys think.