Knight Magus

Thank you for your evaluation, I might make some changes in the future based on your comments, but I dont get what you mean by saying "what benefit or synergy is there in casting more powerful spells as a Magus?" You get half the spells level rounded up as arcane charges so even when you cast a 9th level spell you only get 5 charges, so when you have no charges you could get full benefit from casting even your 9th level spell, of course I get the bad side of this, that you would not want to cast sometimes to not waste those charges for example when you have 2 charges you would not want to cast any spell that would give more than 3 charges assuming 20 int.

Aside from that powerwise capstone is actually pretty good, it prevents a lot of damage, and blade ward is given free just so you would not feel like you have to take it at level 10 and have a cantrip you would never use for 4 levels until you get your capstone, after you get the capstone there should be moments making it worth using to give your tank that resistance especially considering you would be able to make a weapon attack after using it which would probably be the best time to use that arcane charges, Though I wonder if it would be worth using it instead of making another weapon attack with booming blade, depends on the situation I suppose, if there is a change that someone is going to take a burst of damage type that blade ward gives resistance to, it might be worth it.

Walking Fortress is assumed to work with Mage Armor, that is why "while not wearing any armor" wording exists, I was under the impression that mage armor spell would count as not wearing any armor.

Mental Fortress is level 6 feature btw, it seems I have forgotten to include that in its description, I myself have never been satisfied with its second part as well, so I will consider your suggestion when I decide to change it.

I kinda am not in hurry to make the changes because my players did not roll a wizard for our new starting campaign so it might take a while :)

Cheers!

I have a few thoughts on this. You can take it as a critique, or simply inspiration for future iterations, or the useless words of a stranger. No offense taken either way!

First off, I think it's great to have STR be potentially useful for once from Walking Fortress, especially on a Wizard. Would it work with Mage Armor? If so, I wonder if it might help to clear up the wording:

When calculating AC while unarmored, you can add your Strength bonus to your AC instead of your Dexterity bonus.

My only concern is this might make some weird synergy with Monk/Barbarian, but I think it might make for a neat way to make Mage Armor useful for this subclass.

With Spellblade, I really like the idea of it. However, I think any situation with rounding can get kinda rigged. Based on the current writing, the charges are best used for 1st, 3rd, 5th, etc. level, assuming you want to maximize the amount of damage based on the minimum spell levels needed to do so. It sounds kinda funky, but rounding up or down can kinda draw people towards specific spell level casting, in my view. Would it be better to run it at 1d4s equal to the spell slot? Additionally, what benefit or synergy is there in casting more powerful spells as a Magus? It would theoretically cap at level 5, making levels 6 and up less ideal to cast.

Mental Fortress sounds very much like Bladesinger's Bladesong, albeit more constant. I would argue that this is almost a little underpowered. Bladesong can be used twice per short rest, and it's really hard to actually run out of short rests in the day, provided you aren't in the thick of things. In other words, a Bladesinger at level 2 can gain that AC bonus almost all the time, to the point offering it at level 10 to another wizard archetype seems odd. Additionally, I think the secondary part is like a weaker version of War Caster. While I understand that some archetypes (Like Swashbuckler) also gain what are essentially parts of feats, I think that the Knight Magus would be one of those who would very much benefit from that War Caster gives, and thus if they have this feature already, it would make a portion of War Caster useless. Some might argue that it makes War Caster less of a requirement, but I'm of the party that avoiding redundancy would be ideal.

Maybe something like: You gain a bonus to AC and Concentration checks equal to your Intelligence modifier (minimum of 1)? In this way, it all synergizes together in simple terms without making War Caster feel redundant.

Combat Magic is actually pretty fine as it is. It's a little weird compared to Eldritch Knight and Valor Bard, but I think it's still fair in conjunction with everything else going on here.

Knight-Protector is actually the reason I wanted to make this comment. It feels a little weird that, for an archetype capstone, you're getting cantrips and synergy with cantrips and spells. It's pretty cool, but it feels a tad off as a capstone. I would maybe either remove the free Blade Ward from the equation (Because while it is basically a free cantrip, it feels a little disappointing to read), or I may move access to it at a lower level.

The secondary part is something that I was initially okay with, but when I looked up the spell options, there's very little that it realistically synergizes with: Shield, Absorb Elements, and Blade Ward. That is potentially neat, but really not all that exciting. However, I'm not sure what I could suggest, as it would imply that the capstone needs a serious rework.

Hope this is helpful! I'm interested in seeing something like this come to life in a way that is different from Bladesinger, but able to keep up with the power of that archetype.