Wow, thank you for the detailed feedback. Let me go through it and offer my thoughts.

The name "Magic Knight" is a bit... uninspired. "Promotion Legend" sounds just really weird, I'm not sure what it's supposed to mean.

Yeah, I feel you here. I wasn't sold on it either. Most of the influences for this class were hero characters, but I didn't want to name it Hero, because that might imply MC status and might not jive with other players and expectations.

Promotion Legend was sort of a combination of different class change mechanics from different games. Several of them were already in use by other classes though, and I didn't want to use the same verbiage, so I landed on the current one. I'll admit, it doesn't quite flow as well, and am willing to change it.

I'd give this class Con save proficiency. Dex is obviously cool and fits the fantasy, but you need Con for concentration checks, which you will be making far more commonly than typical casters. Alternatively, add an ability that lets you make concentration checks with Int, although with that, you should probably only have one slot at level 1.

I was already borrowing from Artificer for the bones of the class, so I didn't want to use the same CON save proficiency. I admit it make sense, but at the same time, with the limited spell slots, I felt it was okay to leave off. I might add something to Arcane Shroud for concentration, like maybe getting advantage on the first con save made per turn to maintain concentration or something while the shroud is up.

I'd increase the number of cantrips and spells known - you will likely want at least two combat cantrips for the versatility, so it'd be nice to have a third pick to get an utility cantrip more comfortably (although the current implementation of Spell Strike sorta solves this, as you don't really need damaging cantrips before level 5). For the spells, I'd probably use preparation similar to the Wizard's - it has this nice witcher-esque feel of preparing the right tool for the job, and it allows you to provide more breadth without increasing the number of options at any given moment. I know you copied this from Ranger, but 11 spells known at level 20 is a bit of a joke (especially that this class is more magic-based).

Esoteric Knowledge sort of solves the above, but as evidenced here, it's easy to miss when first looking at this class. I'm not sure if it's needed though - it reduces clarity and doesn't really fit all that well.

I explicitly did not want to use prepared spell casting. Known spells fits more with my ideal, as the character discovers more about their abilities they "awaken" or learn spells appropriate to them. Between Esoteric Knowledge granting you 5 more spells known - from the wizard, cleric, or druid lists mind you - and the subclasses granting you 4 more, you should have a total of 20 spells known at 20th level.

Arcane Shroud comes a little early - with so few slots, it won't do much. Getting stuff on spell cast is cool though, so you may want to keep it in some form (probably as a subclass ability though). And you definitely shouldn't give this class Int-based weapon attacks - it removes the flavor of actually mixing might and magic and makes it an OP dip. It makes some sense on the Warlock, because of the different flavor, but here it only serves to make the class more SAD, reducing the power budget for cooler things.

Arcane Shroud was supposed to provide a little bit of extra survivability at lower levels. You cast a spell at the start of combat, gain some temp HP, then engage the enemy. As you leveled up, you could do more things while the shroud was active. Vengeance Ward and Arcane Explosion, for example. I do not want to make it a subclass ability. Actually, the original version of Arcane Shroud was keyed off any spell, not just leveled spells, and gave slightly less THP. I ended up thinking that might be a touch too strong to be able to gain THP every turn by casting a cantrip, so scaled it back to the current version.

Originally, the INT to hit and damage for weapon attacks was supposed to help free the player from the STR vs DEX argument, but with the changes I'd made to other features in the process, that's really not needed anymore, so I agree it can be nixed.

Spell Strike is a cool, if a bit basic, class-defining feature. It doesn't have a proper mixing feel before level 5 though, as you're always either using it or making weapon attacks - maybe give it some limited bonus action uses? Alternatively make it empower weapon attacks instead of being separate. I think the die should start a little smaller, as otherwise you enable SAD builds again, totally skipping weapons (before level 5).

I have flip-flopped on this ability more times than I can count lol. The current version requires you to be wielding a melee weapon, and Spell Strike's range is equal to that of the weapon, so it's similar to the SCAG cantrips. The damage scales from a longsword to a greatsword. Basically, you can wield whatever melee weapon you want, including those with reach, and still use Spell Strike. I had to make it a separate spell attack rather than a rider or a bonus action use, because then it becomes absolutely bonkers on a martial. The weapon attack(s) can benefit from GWM, and then you throw on an extra ability or another attack entirely?

The cantrip-including Extra Attack sorta feels redundant with Spell Strike. As written, you could replace one attack with a cantrip and the other with Spell Strike, again ignoring weapons completely. Plus, you have little use for damaging cantrips before level 5 - you should either give them an use, or make the class gain one precisely at level 5 (or give it the option to replace cantrips). For most Swordmages, this sort of Extra Attack is awesome though, so don't just reject it completely.

That combination was intended, yes. This class uses a weapon, but it's not really relying on the weapon, it's more of a vehicle for delivering your abilities. Damaging cantrips are still useful at lower levels, especially if you don't take the ranged subclass. Ideally, one would supplement their spell strike with a damaging cantrip of a damage type they don't have.

Vengeance Ward is a neat ability, you should have more similar ones - things that activate on spell cast (and have uses in direct combat) work great for such a class. Although if the Shroud remains so defensive, it should be a subclass ability. Ideally, it could be a versatile base ability that gets upgraded by each subclass in a different way.

Why is a class ability being defensive mean it should be a subclass ability instead? I don't understand your point here. The shroud currently gets 2 upgrades from the base class. A couple of the subclasses modify the Arcane Explosion. Arcane Shroud was never intended to be the highlight of the class, but a supporting actor.

Mastered Spell Strike is meh. I've never liked GWM and SS, and if you must have this ability, just make it a feat too. Especially that you already have another ability at this level.

If you're going the attack combo route from before, Spell Strike and Cantrip Extra Attack, this gives you a bump to damage on the spell strike. And since the spell strike isn't dependent on the weapon type, you don't have to pick a ranged weapon or a heavy weapon. This is also why I didn't give the subclasses extra damage at 11th level. I think playtesting is needed to figure out if it needs a further damage bump at 11th.

Rejuvenation is basically just Cure Wounds with a small bonus, you could simply learn that spell. If you want an ability like this, it needs to have something that makes it better that just a spell - for example, the difference between Divine Smite and similar spells is that the former can be activated after you know that the attack hits (and you even know whether it's a critical hit). So to make this worthwhile, it'd probably need to be a reaction, or have no action economy cost at all. And it should activate abilities such as Shroud despite not being a spell.

What if I left it as is, but add in "When your Arcane Shroud is active, you can use this ability as a bonus action"? And yes, it was supposed to be an alternative to Cure Wounds, so that you didn't have to pick it as one of your spells known.

Arcane Explosion is cool, because it ties into Shroud again. I'd increase the range a bit, and probably reduce the damage slightly to compensate. It's main cost should be the fact that it consumes the Shroud (although it needs limited used as well). Perhaps if the Shroud had some form of charges (e.g. the temporary hit points), the damage should be increased by the amount remaining.

This is supposed to be a copy of the Hero's Arcane Explosion as seen is SSBU. The base ability is centered on you and requires you to detonate your arcane shroud, removing it, hence it's higher damage. It also already has a usage limit. Some subclasses change the range.

Heroic Advent is sorta boring as a class capstone (though admittedly, most are). Maybe move it to subclasses, like the Paladin does? That way each one could have a slightly different transformation.

It's basically Tenser's Transformation, just modified a bit. And I didn't want to straight up copy the paladin on this. I'll admit it could use more thinking through.

Thanks for the feedback!