I would like tin hear your ideas.
Alright then - these are not very fleshed out, mind you, and lack a major gimmick or unique selling point, but I'll try my best anyway. Generally speaking, I envision Zael as a swordsman that mixes up his sword attacks with a
lot of kicks. I get that kicks weren't really that major of a thing gameplay-wise in TLS, since Zael only ever kicked in a couple of walls in the game (Syrenne even made a joke about it once, if I recall), but it would make his moveset already a lot more interesting. Not to mention, while there were a lot of weapons in the game that weren't swords, you pretty much had access to the same moveset for all of them, which doesn't really make Zael out to be that unique of a swordsman.
For specific attacks, I'd envision Zael having a
side-tilt and down-tilt similar to Ganondorf's, a
nair and bair just like Link, and a
dair just like Ganondorf's (though alternatively, that could also be for a sword plant attack, like the one he does from walls to diffuse magic circles). His
Up-Smash could also be essentially Ganondorf's pre-sword one, since it isn't really "in use" anymore. These are about all the stand-out attacks for his non-special attacks that come to mind - most of the others I'd say could just use animations similar to those of other swordsmen already in Smash, like the wide forward swinging fair, for example.
Now, for the actual interesting part about this all: The specials.
Neutral Special: Crossbow.
Would function essentially like it does in the game, with Zael kneeling down and firing stuff. Normal shots could be just like, say, Fox or Falco's Lasers. Additionally, there could be a mechanic of Zael switching between various different kinds of ammunition. Like, similar to Shulk's Monado Arts, keep the B button pressed and select the special ammunition from a wheel, which then becomes the new default. Since all of them would be better than standard arrows, though, Zael would only ever get a limited amount of each type. Once he runs out of them, they get put on a cooldown. The different types could be fireworks (traveling in an upward arc), banana peels (which stick around as item similar to Diddy's Down B), paralysis arrows (similar to Zamus' Neutral B minus the charging), burst arrows (could be a much weaker version of Palutena's Explosive Flame), and lastly, annihilator arrows (the ones that only ever appeared in online multiplayer), which could be a huge, fast travelling projectile with a lot of KO power, but you only ever get a very small amount of them (like three, as you get them online, or even just one or two) and they have a long cooldown.
Down Special: Gathering.
I'm admittedly not 100% certain on this could be done, but here's my current idea: Just like how it is in TLS, this is something that you need to activate on your own, at which point a clearly visible blue glowly graphical effect appears on Zael's hand. While it is active, Zael takes more damage (maybe about x1.25 to x1.5 times more), and projectiles slightly home in on him. In exchange, the more damage Zael takes, the more powerful the eventual attack becomes:. Said attack would be a big, hard to avoid shockwave kind of attack, which, depending on the charge, slows down opponents or even outright freezes them for a moment, leaving them open for a follow-up attack, similar to Bayonetta's Witch Time. Since this move could very easily become very broken, though, it would really need to be balanced with great care - full charge could for example only be reached after taking 100% of damage, low charge attacks could have lower range and duration than the higher charges, and so on.
Side Special: Bomb.
Name says it all, really. Zael pulls out one of the bombs that you can occasionally find in the game, and throws them. Could work just like Toon/Young LInk's bombs, though with some minor tweaks.
Up Special: Gale.
Would work similar to how it does in-game. Zael gets in an attack-ready position, a cursor appears on-screen which you move around, and where it stops, he instantly dashes with a windbow. The move could very easily be a mixed bag: On the one hand, the wind bow could easily mess up people, and the dash is very fast. On the other hand, the cursor makes it extremely obvious where Zael recovers to, and he'd be open for attacks while it moves. As to not make it too useless as a recovery, it could slow down his fall if used in the air. Basically. . . think something like Diddy's Up B, with a cursor indicating where you go.
Now, for the Final Smash, there's two options that I'd consider, depending on what "type" of Final Smash would need to be picked.
#1 Final Smash: Ancient Barrier
A combination attack between Calista's Ancient Barrier and Zael's own Accelerate, with Calista making a cameo appearance in order to cast it. Both his movement speed and attack speed would drastically be sped up, while he also receives a huge energy surrounding him that damages and stuns opponents. This is the kind of Final Smash that I would've envisioned him getting in Smash 4. But since Ultimate has an entirely different approach to Fina Smashes, what I'd see as more likely is. . .
#2 Final Smash: Ancient Summon
A more cinematic Final Smash, where at first, Calista appears alongside Zael. She then summons Sentinel Beast Atar, which unleashes a powerful energy attack on the enemy, kinda like Ridley's or K. Rool's Final Smash. Not much to say on that.
For taunts, I also have some ideas:
#1: Zael stricking a pose, and saying "By my honour, I shall do my best!".
#2: Zael doing a standing variation of the. . .
whatever he does when he gets his fortune told.
#3: Zael just tripping and falling. Like he does when tripping on oranges in the city.
For other gameplay mechanics, Zael should be able to wall cling like Sheik or Lucario. Considering his vertical slice, that only seems appropriate.
For alternate costumes, the underwear one is just about a given, considering that Shulk has his. But if Sakurai really doesn't care for spoilers, he could also have Dagran as an alternate costume, since him and Zael have essentially the same abilities. Only his Gathering ability would need to be red. Admittedly though, the Gathering ability that Dagran gets to use in the short portions of New Game Plus where you control him only breaks the ability of enemies to guard, but. . . eh, details. Other than that, Zael could have things like the Knight Armour and various outfits in different colours as alts.
And since I'm already throwing all of my ideas out here, anyway. . . the perfect stage for The Last Story would, in my eyes, be something set on the rooftops of Lazulis City, with a clear view of the colliseum and the castle. For an Assist Trophy, that could be either Zangurak or one of the mage party members, who would fire a magic blast which creates a circle. The obvious choice would be Calista, but she's already part of the Final Smashes that I envision, so using one of the others would bring more variety. The most obvious choice would probably be Yurick, given his decently large role and special ability in the Final Boss fight, but I personally would love Mirania the most, since she's my favourite party member. Lastly, I think that rather than the default Blade/Rune Blade, Zael could use either the Chaos Blade/Stranger, or the Traive.
. . .Alright, that's all I got.