As described in the class description, the subclass features come at levels 3, 7, 11, and 15.

oh i was just skimming and i really dont know

What specific level 15 ability are you speaking of?

Okay, some have mentioned some concerns about the amount of hit points Eldritch Ward give you access to. This post is just to show how many hit points paladins can heal, compared to how many THP the Arcknight can give (the first amount is assuming an Intelligence modifier of +2, and the second is for a +3 to Int, and +4 to Int for the third). 

So, at early levels, it is much more likely for a character to have a relatively low Intelligence modifier, normally a +2 or +3. This makes them normally start out with a bit less Temporary Hit Points from this feature than Paladins can heal with Lay on Hands, but at higher levels they will eventually get quite a lot more THP than paladins can heal. I'm not sure if this is a huge issue, as Temporary Hit Points do not stack, they have to use multiple actions to use this ability, unlike Paladins who can stack all of their healing on the same action. I will have to playtest it to see if this is an issue.

The ability to ignore Concentration saving throws against damage that doesn't reduce to you less than 1 Temporary Hit Point is useful, but not OP, as at level one that will only help against attacks and effects that deal less than 3 damage (most often), and later levels it only works against damage that is less than 24 (with a +5 Int mod), which most monsters at this level can easily do more than. 

I personally really like Eldritch Ward, gives the Arcknight some defender capabilities that I'm assuming may get added on to with one of the subclasses? This reminds me a bit of the 4e Swordmage class which was a mix of a defender and striker. 

I'm still reading through the class and may wait until you post the subclasses before trying out the survey. I want to make sure I have my head fully wrapped around all the mechanics before leaving my full impressions.

Yes, some of the subclasses will add more defending capabilities, but not all of them. It is kind of supposed to be like a Swordmage/Duskblade class, though those will be subclasses of this class. Overall, just an arcane gish half-casting class, kind of like an arcane version of a paladin/ranger, but different enough to fill a class. 

There will be a different survey for the subclasses, but if you want to wait until then, that's fine. 

Okay! Finished a couple subclasses! I've changed when they get their features, though, to separate them from Paladins and Rangers a bit. Now, they get features at level 3, 7, 13, and 19. 

Study of the Swordmage

Commonly practiced among elves, githyanki, dragonborn, genasi, and hobgoblins, the traditional martial study of the Swordmage is an ancient art, tracing its origins back to the ancient empires of mages that used to dominate the worlds (such as the Netheril or Aeor). These mages taught their servants to blend their steel swords and swift spells  into a single, fluid motion, seamlessly merging magic and martial might. 

Swordmage Styles: 

SWORDMAGE STYLES

From the founding of the art of the Swordmage, this way of fighting has been irrevocably connected to swords and other bladed weapons, such as knives and daggers. Specifically, its practitioners most often use Longswords, Katanas, Scimitars, and Sabers, typically with one hand, using the other hand to grapple enemies or hold magic wands. The majority of Swordmages practice a distinct style from the ones listed below, but many blend different styles to create a unique way of fighting. All of these traditional styles have been around since the conception of the Swordmage, tracing their roots back to the first of the members of this art. 

Assault Swordmages. Assault swordmages hold the philosophy that the best defense was a strong offense and protected their friends and allies through aggressive and flashy attacks. In the Forgotten Realms, this style originated on the world of Abeir, being brought to the world of Toril during the Spellplague, whose users channel energy from the Elemental Chaos to power their attacks with heavy weapons. While they placed an extremely high value on intelligence, assault swordmages considered physical strength of utmost importance, using their strength of body and mind as one to enhance the potency of their attack spells. Typically, assault swordmages preferred the use of heavy blades such as greatswords or greataxes, or occasionally double-bladed scimitars, though as a consequence they tended to put a smaller emphasis on their own defense. Goliath and Orc swordmages often choose this style.

This often lead to them taking the Great Weapon Fighting or Arcane Warrior fighting style, concentrating on making the most out of their assaulting attacks instead of protecting themselves or others. They also frequently would focus on evocation magic, merging powerful elemental spells, such as fireball or thunderwave, into their already powerful attacks. Recommended feats for characters that practice this style are Fighting Initiate, Great Weapon Master, Martial Adept, Savage Attacker, and War Caster. 

Shielding Swordmages. Where assault swordmages preferred brute force, shielding swordmages preferred the use of magic as a shield against harm. Like all swordmages, shielding swordmages were often extremely cunning foes, but they were are quite often immensely durable, a quality they use to enhance some of their spells while also allowing them to take blows that their allies would otherwise suffer. However, shielding swordmages did not solely rely on their constitution to preserve them and in all things they preferred a strong defense. As a result, shielding swordmages generally preferred one-handed blades such as longswords and battleaxes, allowing them to parry their foes more easily than a larger weapon would easily allow, also allowing them to use a shield. Elven, Dwarven, Goblin, and Githyanki Swordmages typically use this style of fighting. 

Due to their preference of using a sword and shield, Shielding Swordmage characters should use the Dueling or Protection Fighting Styles. They also focus on abjuration and protection magic, such as the shield, blade ward, protection from energy, and wall of force spells. Recommended feats for swordmage characters of this style are Defensive Duelist, Dual Wielder, Sentinel, Shield Master, and Tough. 

Wandering Swordmages. It is rumored that this style is among the first practiced by the Swordmages. Wandering swordmages possess a vast knowledge of a variety of subjects that spanned the various realms of the multiverse. They created their own style of fighting of based on insights they gleaned from these diverse cultures and learned spells that may not normally be uncovered by other swordmages. They were quick learners, wise enough to learn lessons from the histories of others and apply the knowledge to their own skill as combatants. Wandering swordmages saw events and conflicts from multiple points of view and gained perspective from every local fable, academic lesson, philosophical perspective or bit of lore they picked up in their travels. This causes them to often use thrown weapons or unarmed strikes, such as daggers, spears, tridents, and handaxes. Wood Elf, Triton, Shifter, Lizardfolk, Firbolg, Bugbear, and Satyr Swordmages typically are members of this style.

Swordmages of this style typically take the Thrown Weapon Fighting or Unarmed Fighting Fighting Styles, as they typically use thrown or natural weapons. They don't focus on any specific school of magic, but often use the expeditious retreat, misty step, and fly spells, focusing on mobility so that they can get into range for their attacks. Recommended feats are Athlete, Charger, and Mobile. 

Primordial Paths:

PRIMORDIAL PATHS

Distinct from Swordmage Styles, which any Swordmage can take independent of their world, not every setting that has Swordmages has Primordial Paths. A Primordial Path is typically specific to worlds closely linked to elemental powers, such as Abeir, Athas, and the Elemental Planes. Any style of Swordmage may pick any Primordial Path in this world, but it is more common for Assault Swordmages to choose a Primordial Path than the other styles. 

Astropomancy. Astropomancy is the path that focuses on blending the magic of the storm with their weapon attacks. These Swordmages typically use shatter, thunderwave, witch bolt, lightning bolt, thunder step, and other similar spells. 

Nephomancy. The Swordmages of the primordial path of nephomancy focus on blending pure cold with their powerful strikes, slaying their enemies with freezing strikes. Spells typically used by Swordmages of this path are frost fingers, cone of cold, and other cold-damaging spells. 

Pyromancy. Fire is the preferred element of pyromancing Bladesingers, merging their attacks with burning fire, incinerating their enemies into oblivion. Spells favored by these Swordmages are fireball, burning hands, immolation, scorching ray, and other flaming spells. 

Vitriomancy. Blending acid and attacks together, practitioners of this style melt their enemies with powerful acidic might. Due to this, they typically use dissolving spells, such as acid arrow, vitriolic sphere, and other acidic spells. 

Study Spells

3rd-level Study of the Swordmage feature

Study of the Swordmage Spells

Transient Steps

3rd-level Study of the Swordmage feature

Your ability to blend your martial ability with your arcane magic allows you to become magically mobile. Immediately after you cast a spell or release it through your Spell Strike feature, immediately after you cast it, you may teleport an amount of feet equal to 1 + the spell's level, the total amount multiplied by 10. You may do so only once a turn. 

Sword of Phasing

7th-level Study of the Swordmage feature

Once a turn, when you hit a creature with a weapon attack on the same turn that you have teleported to a space within 10 feet of this target, the attack deals an extra amount of force damage equal to your Intelligence modifier (minimum of one damage).

Teleporting Expert

13th-level Study of the Swordmage feature

When you cast a spell that allows you to teleport that required you to expend a spell slot of 2nd-level or higher, as long as the spell does not deal damage, you may regain one expended spell slot. The slot you regain must be of a level lower than the spell you cast. 

Additionally, immediately after you cast a teleportation spell, your Armor Class increases by your Intelligence modifier until the start of your next turn. 

Swordmage Master

19th-level Study of the Swordmage feature

Your ability to merge magic, movement, and martial power increases, granting you the following benefits:

• Immediately after a creature you hit with an opportunity attack stops moving, you may teleport to an unoccupied space of your choice within 10 feet of them.
• As part of the action used to cast a teleportation spell, immediately before or after the spells effects are released, you may make one weapon attack with your Infused Weapon. 

Study of the Eldritch Nullifier

The study of the Eldritch Nullifier is practiced by the Arcknights who choose to use their arcane power to prevent others from casting spells. Typically bounty hunters and zealots who specialize in tracking down and slaying mages or bodyguards and mercenaries that focus on protecting their clientele from magic users, Eldritch Nullifiers are usually rare, but are highly valued for their powerful capabilities at mage-slaying. 

Study Spells

3rd-level Study of the Eldritch Nullifier feature

You gain the following prepared spells, which become arcknight spells for you and do not count against the amount of spells you can prepare. 

Study of the Eldritch Nullifier Spells

Spell Stopper

3rd-level Study of the Eldritch Nullifier feature

When a creature makes a Constitution saving throw for concentration that you forced them to make, they have disadvantage on the saving throw. 

Annulling Strikes

9th-level Study of the Eldritch Nullifier feature

When you hit a creature that willingly has a spell cast on them with an attack using your Spell Strikes, as long as they weren't concentrating on the spell, you may force the creature to make a Constitution saving throw for concentration against your spell save DC, ending the spell's effects on them on a failed save. 

Block Magic

13th-level Study of the Eldritch Nullifier feature

Once a turn, when you hit a creature with a weapon attack using your Infused Weapon, you may mark them with a Nullifier's Brand. This brand lasts until the start of your next turn or until it is removed by a remove curse or greater restoration spell. While this brand lasts, they are incapable of casting any spells and any spell cast on them has no effect until the brand ends. 

You may use this an amount of times equal to your Intelligence modifier (minimum of once), regaining all expended uses at the end of a long rest. 

Antimage

19th-level Study of the Eldritch Nullifier

You gain the following benefits:

• When you use Spell Siphon, the level of spell slot you steal can be of any level, and you gain a spell slot of the level you choose to steal or lower until you finish a long rest. 
• Once a turn, when you hit a creature with an attack that has the ability to cast a spell, you deal extra damage equal to your Intelligence modifier (minimum of one extra damage). 
• As a reaction, when a creature within reach of a magical melee weapon you're holding casts an offensive spell, you may make an attack with that weapon against them. If you hit, their spell does not come into effect and is wasted, and you imbue that spell into your weapon as with your Spell Strike ability. 

Okay, any thoughts on the first two subclasses before I do the others?

Okay, just did a major nerf to Spell Strike. Now, if you attack with the weapon that has Spell Strike in it, the spell is lost at the end of your next turn. Additionally, cantrip damage does not scale as it normally would, to limit the abusability of these spells with this feature at later levels. I hope that helps balance it a bit more. I also got rid of the Unarmed Strike features, so I will probably make a subclass for that. 

Quote from Third_Sundering >>

What specific level 15 ability are you speaking of?

 i was just thinking that rouges get blindsight at level 15

The Blind Fighting style is (according to the leaks) exactly the same as it will be in Tasha's. Whether or not it is better than a Rogue ability at 15th level doesn't really matter, as they have to give their Fighting Style to take it. 

Got more subclasses done! I'm trying not to go overboard while simultaneously giving quite a few important character choices, to make it so different and more diverse types of characters is easier as an Arcknight. I will probably just make three or four more subclasses, the Bastion, the Punchy-fire-arcknight subclass (working on name), and a dunamancer Arcknight. 

Study of the Element Herald

Elemental Heralds harness their practiced arcane power to blend their weapon attacks with powerful elemental energy. Unlike most other elemental practitioners, these Arcknights are not bound to any specific element, easily accessing all elemental damages at any given moment. 

Study Spells

3rd-level Study of the Element Herald feature

Study of the Element Herald Spells

Primordial Striker

3rd-level Study of the Element Herald feature

When you cast a spell that deals acid, cold, fire, lighting, or thunder damage, with the spellcasting focus being your Infused Weapon, you may change the damage type it deals to any other damage type from that same list. 

Empowered Elements

7th-level Study of the Element Herald feature

Once a turn, when you cast an Arcknight spell that deals acid, cold, fire, lightning, or thunder damage, you may deal an extra 1d8 damage of that type. 

Element Scholar

13th-level Study of the Element Herald feature

When you see a creature cast a spell of a level that you can cast that deals acid, cold, fire, lightning, or thunder damage, you may use a reaction to instantly prepare/know the spell, not counting against the maximum amount of spells you can prepare or know. You may know an amount of spells this way equal to your Intelligence modifier (minimum of one spell). If you already know the maximum amount of spells you can know from this feature, you can choose one spell you know this way to forget, replacing it with the spell that triggered this reaction. 

You know spells granted by this feature until you choose to forget it at the end of a long rest. 

Elementalist

19th-level Study of the Element Herald feature

You gain the following benefits: 

• You gain resistance to acid, cold, fire, lightning, and thunder damage. 
• Once a turn, when you deal acid, cold, damage, fire, lightning, or thunder damage, you may reroll an amount of damage dice of that damage type equal to your Intelligence modifier (minimum of once dice). You must use the new roll. 

Battlemage

A Battlemage is an Arcknight who focuses on blending the powers of wizardry with martial combat, granting them unique powers and abilities that set them apart from all other casters. They strive to be paragons of arcane casting, nearly rivaling the eldritch power and versatility of wizards.

Study Spells

3rd-level Study of the Battlemage feature 

You gain study spells at the Arcknight levels listed. When you take a long rest, you may replace any of the spells granted by this feature with any wizard spell of the same level as the spell you replace. 

Spellcasting

When you reach 3rd level, you have studied long and hard to become more practiced with spellcasting than other arcknights. This allows you to be more adept with spellcasting, increasing your power over arcane spells.

Cantrips

You learn two cantrips of your choice from the wizard spell list. You learn an additional wizard cantrip of your choice at 10th level. These count as arcknight spells for you. 

Spell Slots

The Battlemage Spellcasting table shows how many spell slots you have to cast your arcknight spells of 1st level and higher. This table replaces the typical amount of spell slots you would have, as shown on the Arcknight Class table. As normal, you regain all expended spell slots when you finish a long rest.

Battlemage Spellcasting

Battlecaster

3rd-level Study of the Battlemage feature

Due to your prowess with arcane power, you gain the following benefits:

• You may attune to magic items that require attunement by a wizard. 
• When you regain spell slots on a short rest due to your Arcane Recovery feature, you may regain spell slots equal to half your arcknight level (rounded up). 
• You can cast an arcknight spell as a ritual if that spell has the ritual tag and you have the spell prepared.

Arcane Smite

7th-level Study of the Battlemage feature

Once per turn when you hit a creature with your Infused Weapon, you can expend a spell slot to deal an extra 1d8 force damage to the target, plus another 1d8 per level of the spell slot. Additionally, if the target is a creature that is Huge or smaller, they become restrained until the end of your next turn. 

Eldritch Mage

13th-level Study of the Battlemage feature

When you prepare a spell, it can be from the arcknight or wizard spell list, and counts as an arcknight spell for you. You may not replace a spell granted by your Study Spell feature this way. 

Battlemage

19th-level Study of the Battlemage feature

You gain the following benefits: 

• Choose one first level spell from the wizard spell list that you have prepared. For you, it is always prepared and doesn't count against the amount of spells you can have prepared. You may cast this spell at its lowest level without expending a spell slot. If you want to cast the spell at a higher level, you must expend a spell slot as normal.
• As an action, you may regain one expended spell slot of 3rd-level or lower. You may use this feature twice, regaining all expended uses when you finish a long rest. 

Study of the Duskblade

The majority of Arcknights are members of the Study of the Duskblade, as it is the least specialized of the Arcane Studies, focusing more on using bladed weapons and striking than other esoteric arts. This is due to the fact that this study was the first developed by the original Arcknights, and is easier to master than other Arcane Studies. Duskblades focus on battlefield control and weakening enemies, as well as pure, obliterating power. 

Study Spells

3rd-level Study of the Duskblade feature

Study of the Duskblade Spells

Swift Infuser

3rd-level Study of the Duskblade feature

You are a master of imbuing spells into your Infused Weapon. When you hit a creature with an attack roll with your Infused Weapon that has your Spell Strike feature applied to the attack, if you are still holding your Infused Weapon, you may immediately use your reaction to cast a spell that has a casting time of one action, imbuing it into your Infused Weapon with your Spell Strike feature. The spell may not be released until your next turn. 

You may use this feature an amount of times equal to your proficiency bonus, regaining all expended uses when you finish a long rest. 

Powerful Strikes

7th-level Study of the Duskblade feature

Once a turn, when you hit a creature with an attack that releases a spell from your Spell Strike feature, the attack deals an extra 1d8 damage of the weapon's or spell's type (your choice). 

Unsettling Blade

13th-level Study of the Duskblade feature

When you hit a creature with an attack that releases a spell from your Spell Strike feature, you do not provoke opportunity attacks until the end of your turn. 

Striker

19th-level Study of the Duskblade feature

You gain the following benefits: 

• You are immune to damage dealt by spells released through the Spell Strike feature. 
• When you deal damage with a spell with your Spell Strike feature, you may cause the spell's damage dealt to the creature hit with this attack to deal the most damage possible, instead of rolling. You may use this features once a long rest.

Okay, that's it. I will probably add more later this week. 

Any thoughts on the subclasses? I've changed my mind, and am currently adding them to the survey (it has no responses yet). 

I'm looking over the class and subclasses right now. Will you be adding Interception to the list of Fighting Styles?

Thanks for doing so! I await your response. 

Yes, I will do so right now. That fighting style fits perfectly with certain archetypes of a Swordmage/Duskblade. Thanks for the suggestion! 

If there are any other features/spells from Tasha's that you or anyone else thinks should be in the class, I'll consider adding them. 

Okay, I just added Interception to the Fighting Styles and added an arcane version of it (works similarly to Hellish Rebuke, now). 

As far as spells from Tasha's is concerned, maybe Spirit Shroud or Tasha's Caustic Brew. Otherwise I'm not really sure about the rest.

Okay, I added tasha's caustic brew and intellect fortress. I considered adding spirit shroud, but I don't think it fits the overall theme that well. I will probably add it to a subclass later, probably a death knight themed one.

Alright, I'm done with the Arcknight Survey. I hope some of that is helpful.

Thanks so much! I'll make the survey for subclasses later today, hopefully.