Base Class: Artificer
While every Artificer tinkers with merging arcane magic and mechanical devices, an Archanomechanist specializes in using their knowledge of the arcane and the mechanical arts to assemble a device that can augment their own physical capabilities. This device—known as an archanomecha, or mech—enables the Archanomechanist to readily engage in physical combat, with the archanomecha providing the strength for their blows and helping to shield them from harm.
Archanomechas vary greatly in appearance and form. Some are built like a hulking automaton, but with the addition of a cockpit canopy containing a control panel of buttons and levers. Others are archanomechanical suits of power armor, whose movements mimic those of the wearer and enhance them with archanomechanical force.
Tool Proficiency
When you adopt this specialization at 3rd level, you gain proficiency with smith's tools. If you already have this proficiency, you gain proficiency with one other type of artisan’s tools of your choice.
Archanomechanist Spells
Starting at 3rd level, you always have certain spells prepared after you reach particular levels in this class, as shown in the Archanomechanist Spells table. These spells count as artificer spells for you, but they don’t count against the number of artificer spells you prepare.
Archanomechanist Spells
Artificer Level | Spell |
---|---|
3rd |
|
5th |
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9th |
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13th |
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17th |
Battle Hardened
When you reach 3rd level, your combat training and your experiments with mechanically assisted combat have paid off and you gain proficiency with martial weapons. You also learn the mending cantrip, which doesn’t count against your number of cantrips known.
Archanomecha
By 3rd level, your tinkering has borne you an archanomecha, or "mech", which is a construct you can verbally command, or mount and control directly. You determine the archanomecha's appearance: it may have a fully enclosed chassis with a canopy atop with a seat and control panel, or it may be a hollow, close-fitting, archanomechanical suit of power armor; your choice has no effect on its game statistics. However it is formed, it contains a space (referred to as its cockpit) which is the same size as you, from which it can be controlled by a creature (referred to as its pilot). It is friendly to you and your companions, and it obeys your commands. See this creature’s game statistics in the archanomecha stat block.
Might of the Master
Your archanomecha has hit points equal to five times your level in this class + your Intelligence modifier + the mech’s Constitution modifier. Its skill and saving throw bonuses increase by 1 whenever your proficiency bonus increases. When you reach 4th, 8th, 12th, 16th, and 19th level in this class, you can increase one of your archanomecha's ability scores of your choice by 2, or you can increase two ability scores of your choice by 1. You can’t increase your mech's ability scores above 20 using this feature.
Cockpit
The archanomecha has an interior space the same size as you, referred to as its cockpit. If the cockpit is unoccupied, any creature of this size or smaller which is within 5 feet of the mech can mount it and enter the cockpit by spending half their movement. While inside the cockpit, a creature has half cover from any threats external to the mech. Use the rules for mounted combat (see "Mounted Combat" in chapter 9 of the Player’s Handbook) unless otherwise stated. When a hostile creature mounts the archanomecha, the mech can use its reaction to shake the creature off. The creature must succeed on a DC 14 Dexterity saving throw, or take 1d6 bludgeoning damage and be knocked prone.
Pilotable
When you enter the cockpit of your archanomecha, you immediately take control of it (no action required). Any other humanoid creature mounted inside the cockpit of the archanomecha can spend their action to attempt to gain control of the mech. The creature must succeed on an Intelligence check with DC equal to 12 + your Intelligence modifier. On a success, the creature assumes control of the mech until the creature dismounts or is incapacitated. A creature controlling the mech from within its cockpit is referred to as its pilot. A pilot can not wield a shield or weapon while controlling the mech.
Archanomechanical Arms
The archanomecha has two arms. The primary arm can wield any simple or martial melee weapon which does not possess the two-handed property. The secondary arm can wield any melee weapon which possesses the light property. Its unarmed strikes deal bludgeoning damage equal to 1d6 + its Strength modifier. When a pilot commands the archanomecha to make an attack using a weapon with which the pilot is proficient, add the pilot's proficiency modifier to the attack roll, in addition to the mech's Strength modifier. Use the mech's Strength modifier for its weapon damage rolls.
Combat
With a pilot. The archanomecha shares initiative count with the pilot and takes its turn at the same time as the pilot. The archanomecha can take any action listed in its stat block in addition to those listed in the "Actions In Combat" section in chapter 9 of the Player’s Handbook. While it is being piloted it can also take a bonus action, using one of the options indicated in its stat block. However, the archanomecha can take an action, bonus action, and reaction only at the cost of its pilot's action, bonus action, and reaction, respectively. If the mech wields or carries an item which requires attunement, it gains the specified magical benefits of the item only if the pilot has attuned to the item.
Without a pilot. The archanomecha shares initiative count with you and takes its turn at the same time as you. You can verbally command the archanomecha where to move (no action required). The only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to verbally command it to take the Repair action described in its stat block or the Dash, Disengage, Help, Hide, or Search action. While it lacks a pilot, the mech can take one action and reaction each round, but no bonus action. If the mech wields or carries an item which requires attunement, it gains the specified magical benefits of the item if you have attuned to the item.
The archanomecha can take at most one action, bonus action, and reaction per round of combat, even if its controller changes during a round of combat.
Mendable
If the mending spell is cast on the archanomecha, it regains 2d6 hit points. If it has died within the last hour, you can use your smith's tools as an action to revive it, provided you are within 5 feet of it and you expend a spell slot of 1st level or higher. The archanomecha returns to life after 1 minute with all its hit points restored.
At the end of a long rest, you can create a new archanomecha if you have your smith’s tools with you. If you already have an archanomecha from this feature, the first one immediately perishes.
Spellcasting Focus
While you are piloting your archanomecha, you can use it as a spellcasting focus for your artificer spells. When you cast spells in this way, spells which would originate from the caster originate from the mech instead. When you cast a spell which affects all creatures within an area except for the caster, such as thunderclap, they affect neither you nor the mech.
Once you reach 11th level, you may use your Spell-Storing Item feature to store a spell in your mech. When a spell is stored in the mech, its pilot can use their action to produce the effects of the spell. If the spell requires concentration, the pilot must concentrate on it.
Share Spells
When you use your archanomecha as a spellcasting focus and cast an artificer spell targeting yourself, you can choose to have the spell also affect your mech.
Archanomechanical Infusions
Some artificer infusions which affect items can also be used to infuse your archanomecha. If you know one of these infusions, listed below, you can use it to infuse your archanomecha. If you imbue it with one of your artificer infusions, the archanomecha counts towards the number of objects you can infuse. An archanomecha can bear no more than one magical infusion at a time.
Tip: Adding your archanomecha to your character sheet
To add your archanomecha to your character sheet in dndbeyond, do the following:
- Add the archanomecha homebrew monster to your collection.
- Navigate to your Archanomechanist character sheet. Refresh the page if it was open before you added the archanomecha to your collection.
- Go to Extras > Manage Extras.
- Choose category "Battle Smith Defender".
- Untick the checkbox "Filter Using Battle Smith Defender Rules".
- Type archanomech into the search box, and click Add next to the appropriate entry.
Adding your archanomecha in this way will ensure its maximum hit points and skill proficiencies scale up automatically as your character advances in level. Unfortunately, the Ability Score Increase for your archanomecha can't be implemented in dndbeyond, and you will have to keep track of those yourself.
Archanomechanical Inventor
You are always striving for ways to improve your archanomecha.
When you reach 5th level, you develop two designs which can be used to improve your mech, choosing from the Archanomechanical Designs section at the end of this subclass's description. You learn two additional designs of your choice when you reach 9th level, and two more once you reach 15th level.
Whenever you gain a level in this class, you can replace one of the archanomechanical designs you learned with a new one.
Prodigious Inventor
When you reach 9th level, you learn two additional designs for your archanomecha.
Prolific Inventor
When you reach 15th level, you learn two additional designs for your archanomecha.
Archanomechanical Designs
The archanomechanical designs are presented below, in order of prerequisite level. If a design specifies a minimum artificer level, you can’t learn such a design until you are at least that level in this class.
When you learn a new archanomechanical design, you can incorporate it into your archanomecha the next time you complete a long rest, provided you have your smith's tools with you. You can integrate all the designs you know into the same archanomecha.
Each design you know is optional, and can be omitted from your archanomecha if you choose not to utilize it. For example, if you know the Giant Mech design, you can choose whether to build a giant archanomecha or a standard archanomecha.
Extra Mech Attack
When you spend your action to command your archanomecha to make a weapon attack, it can make two attacks instead of one.
Reinforced Plating
Your archanomecha gains a +1 bonus to its Armor Class. The bonus increases by one when you reach 9th level (+2), 13th level (+3), and 17th level (+4) in this class.
Secure Cockpit
Any creature mounted inside the cockpit of your archanomecha has advantage on saving throws against being dismounted, and three-quarters cover from external threats.
Spellcannon Attachment
Whenever you cast an artificer spell using your archanomecha as a spellcasting focus, you gain a bonus of 1d8 to one of the spell’s damage rolls.
Agile Mech
Prerequisite: 9th level
You can create an agile archanomecha.
- The speed of your archanomecha increases to 40 feet.
- Its Dexterity score increases by 4, and Strength decreases by 2.
- It can wield ranged weapons in one or both arms, and it can wield a two-handed weapon if it uses both its arms to do so.
- The DC of its Shake Off reaction increases by +2 (to 16).
If you also know the Giant Mech design, you can choose to create an agile giant archanomecha instead.
Enhanced Repair
Prerequisite: 9th level
When the mending spell is cast on your archanomecha, or it uses its Repair action on itself, it recovers additional hit points equal to your Intelligence modifier (minimum of 1). Also, your archanomecha can use its Repair action once more each day.
When you reach 15th level in this class, you gain one further use of the archanomecha's Repair action.
Giant Mech
Prerequisite: 9th level
You can create a giant archanomecha.
- The size of your archanomecha increases from Medium to Large.
- Its Strength and Constitution scores increase by 1, to a maximum of 21.
- It can wield any melee weapon in its primary arm, and any weapon without the two-handed property in its secondary arm.
- The damage of its unarmed strike increases to 1d8 + its Strength modifier.
- The cockpit of the giant archanomecha is elevated 10 feet off the ground. If a creature piloting the mech is dismounted, they fall 10 feet (1d6 bludgeoning damage). Melee combatants at ground level need at least a 10-foot reach to directly engage with a creature inside the cockpit.
- The DC of the archanomecha's Shake Off reaction increases by +2 (to 16), and its damage increases to 2d6.
If you also know the Agile Mech design, you can choose to create an agile giant archanomecha instead.
Self-Destruct
Prerequisite: 9th level
As a bonus action, you can verbally command the archanomecha to detonate if you are within 60 feet of it. Doing so destroys the mech and forces each creature within 20 feet of it to make a Dexterity saving throw against your spell save DC, taking 3d8 force damage on a failed save or half as much damage on a successful one. Any creatures inside the cockpit of the mech automatically fail the saving throw.
Shocking Strike
Prerequisite: 9th level
When your archanomecha hits a target with a weapon attack or unarmed strike at your command, you can channel electrical energy through the attack. The target creature makes a Constitution saving throw against your spell save DC. On a failed save, the creature takes an additional 2d8 lightning damage and is stunned until the end of your next turn. On a successful save, the creature takes half as much damage and isn't stunned. The target has disadvantage on the save if they are wearing armor made of metal.
Once you use this feature, you must finish a short or long rest before you can use it again. Starting at 15th level, you can use it twice before a rest, but only once on the same turn.
Mega Mech
Prerequisite: 15th level, Giant Mech
You can create a mega archanomecha.
- The size of your archanomecha increases from Large to Huge.
- Its Strength and Constitution scores increase by 1, to a maximum of 22.
- It can wield any melee weapon in either of its arms.
- The damage of its unarmed strike increases to 2d4 + its Strength modifier.
- The cockpit of the mega archanomecha is elevated 20 feet off the ground. If a creature piloting the mech is dismounted, they fall 20 feet (2d6 bludgeoning damage). Melee combatants at ground level need at least a 20-foot reach to directly engage with a creature inside the cockpit.
- The archanomecha's Shake Off reaction affects all creatures attempting to mount it until the start of its next turn, and its damage increases to 3d6. The creature triggering the reaction has disadvantage on their save.
If you also know the Agile Mech design, you can choose to create an agile mega archanomecha instead.
Recurrent Memory Module
Prerequisite: 15th level
Your archanomecha's Intelligence score increases by 2.
If you have used your Spell-Storing Item feature to store a spell in your archanomecha, as a bonus action you can verbally command it to use its action to produce the effect of the stored spell whenever it does not have a pilot. If the spell requires concentration, the archanomecha must concentrate on it.
If a pilot of your archanomecha commands it to produce the stored spell and the spell requires concentration, they can choose whether to use their own concentration or the archanomecha's concentration.
Invulnerable Plating
Prerequisite: 17th level
Your archanomecha gains resistance to bludgeoning, piercing, and slashing damage from nonmagical weapons.
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This is awesome! I just wish there was a garguantuan upgrade for level 20. That would be awesome.
Wow this subclass looks awesome!
I had a couple ideas for additional modifications for mecha: (A bit of background; when I think of a mecha, I'm thinking of the clankers from Ian Irvine's The Well of Echoes series - 6 legged war wagons carrying troops and supplies, with externally mounted weapons)
Ballista attachment (this would probably require a giant or mega mecha design frame, and may be mutually exclusive with the spellcannon)
A barricade option that the mecha can transform into on command, creating a small wall (or a larger wall if it is a giant or mega mecha)
A tank mecha design (this would be an mutually exclusive with the agile mecha, being the exact opposite - sacrificing agility for strength and HP)
A harpoon attachement, to be used for crossing chasms or pulling enemies closer
a transport module for giant or mega mecha, which allows it functions as a vehicle the party can ride on or carry excessive amounts of loot in.
A turret mode the mecha could transform into, for increased firepower at the cost of mobility (may be mutually exclusive with other options)
I really like this subclass! Sitting here reading it to another DM now. You can really tell you put in a lot of work, and I love that you even made the creature stat block for each version. Awesome job!
Could you go into more detail about the Share Spells feature and the Spellcasting Focus feature?
I'm specifically wondering about how it interacts with spells like Shield, which you get automatically prepared as part of the subclass. If you're in the Archanomecha, it's unclear whether the clause that says you can cast self spells from the Mech's space allows reaction spells to proc off of the Archanomecha. For example, if your Archanomecha were to be hit with an attack or magic missile spell, would the Share Spells and Spellcasting Focus features allow you to cast Shield affecting the Archanomecha to give it +5 to AC?
It seems to me that's the intent behind you getting the Shield spell as an automatically prepared spell from the subclass, since otherwise, you'd mostly not get any use out of it since the enemies are probably gonna hit the Archanomecha and not the PC, and if they ever do hit the PC, you're most likely not making use of the rest of the subclass. But, if I'm wrong, please correct me.
Can a non-creator enter the cockpit if it isn't on the top, but is inside the archanomecha? It seems to reference being on top of the archanomecha and mounting it. Is that simply a technical term or is it referring to the version of the archanomecha in the form of a mountable animal?
Just make the character sheet without D&D Beyond.
This looks like an actual subclass, getting a subscription soon and this is at the top of my list on homebrew I am getting.
This subclass on its own makes me want to get a subscription to D&D beyond just so I can play it.
Thanks for reminding me, I will try to make the time to issue an update incorporating some of the feedback I have received. I can't guarantee it will be soon though, as I have a lot on at the moment.
Will there be any further updates to this class? Looks amazing and will be starting a character with it soon.
Glad to hear you've been enjoying it!
No, I'm not planning on making another Mech design. I think being able to pick a different mech variant is cooler and more fun. But every time I create a new mech variant, I also have to make one for every combination with all the other mech variants too; and I think having too many mech creatures to pick from is more unwieldy for the player as well. There are currently 6 archanomechas, and I'd have to increase this by another 6 to handle all the combinations with another mech variant (Caster Mech, Giant Caster Mech, Giant Agile Caster Mech, ...). Because of this I only want to make a new mech variant when there are multiple changes incorporated into the new design. For instance, I could have made a new variant mech for the Enhanced Repair or Recurrent Memory Module designs, but chose not to because they are not sufficiently complicated to necessitate it. Of course, for balance a new design which does a many of things at once can only do many small things and/or incorporate negative effects as well as positive ones (Agile Mech reduces Strength, bigger mechs come with a risk of fall damage). I don't think there is a need for one specifically to enhance casting.
What I might add is another option to enhance casting at 9th level, to fill the hole for caster options (5th: Spellcannon Attachment, 15th: Recurrent Memory Module). I'm thinking this will be like Empowered Spell for Sorcerers and let you re-roll damage on spells cast through the mech a limited number of times per day.
that is a much better idea than mine, as mine had the possibly of being to powerful.
So I've been playing this subclass recently and been loving the heck out of it. Only thing I'm curious about is if you had considered making some variant of the agile/huge/mega design upgrades centered on those who want to focus wholly on caster combat.
Possibly... what level do you think the capstone should be available?
The Class Feature Variants Unearthed Arcana adds Spellcasting Versatility for Bard/Ranger/Sorcerer/Warlock and Maneuver Versatility for Battle Master Fighters, letting players swap out one spell/maneuver known on a long rest instead of just when they level up. If you're using that rule set I think it would make sense that the Archanomechanist can swap out one Archanomechanical Design known on a long rest. I think this would probably be a better solution as it increases the versatility (and makes the versatility available before reaching the capstone), but it does take a few days to completely overhaul how your mech is built if you want to change multiple designs.
I would do a capstone where you have access to all of the designs, but can only use 6 at once on the mech, partially cause some of them dont become available when you are granted the ability to take the, and partially cause this appears to be a pretty adaptable build, and that goes more towards that philosophy.,
Yes, you just pick regular weapons to give the archanomecha to wield... but those are bad examples of weapons since both of them possess the two-handed property so neither of them can be wielded by the base archanomecha, and only agile archanomechas can wield a crossbow.
Example weapons for the base archanomecha (which is the only version available until you reach 9th level) are the longsword as a primary and the shortsword as a secondary weapon. When you reach 9th level you can choose the Agile Mech and/or Giant Mech designs which increase the range of weapons which your archanomecha can wield.
I've drawn up a table below showing which weapons are possible for which archanomecha variants.
archanomecha
melee: not two-handed
(e.g. longsword)
ranged: none
melee: light only
(e.g. shortsword)
ranged: none
none
agile archanomecha
melee: not two-handed
(e.g. longsword)
ranged: not two-handed
(e.g. hand crossbow, sling, net)
melee: light only
(e.g. shortsword)
ranged: light only
(i.e. hand crossbow)
melee: any
(e.g. greatsword)
ranged: any
(e.g. longbow, heavy crossbow)
giant archanomecha
melee: any
(e.g. greatsword)
ranged: none
melee: not two-handed
(e.g. longsword)
ranged: none
none
agile giant archanomecha
melee: any
(e.g. greatsword)
ranged: any
(e.g. longbow, heavy crossbow)
melee: not two-handed
(e.g. longsword)
ranged: not two-handed
(e.g. hand crossbow, sling, net)
none
(anything which can be wielded using both arms can be wielded using just the primary arm)
mega archanomecha
melee: any
(e.g. greatsword)
ranged: none
melee: any
(e.g. greatsword)
ranged: none
none
agile mega archanomecha
melee: any
(e.g. greatsword)
ranged: any
(e.g. longbow, heavy crossbow)
melee: any
(e.g. greatsword)
ranged: any
(e.g. longbow, heavy crossbow)
none
(anything which can be wielded using both arms can be wielded using either arm alone)
Initially the archanomecha can't wield a greatsword or a crossbow because it doesn't have the dexterity to put its hands together and hold one of these weapons with both arms (you can't clap a round of applause in a base archanomecha). What you gain instead is the ability to attack with each arm separately, and add your mech's Str modifier to attacks made with your secondary weapon when you attack with it as a bonus action. This is effectively a better version of the Two-Weapon Fighting Style, since you gain this benefit when you attack as a bonus action no matter what you do with your action (you can cast a spell as an action, or attack with a weapon which isn't light).
When you progress to 9th level, you can make your archanomecha bigger and stronger so it can wield any melee weapon in just its primary hand. Or you can make it more agile so it can clap, hold a big weapon using both hands, and it has the dexterity to use ranged weapons.
At 15th level you can make the mech even bigger (huge) and it can dual wield a pair of greatswords, or (if it is also agile) dual wield a pair of heavy crossbows.
I hope that helps! Let me know if you have any further questions.
Do I just do a weapon like a great sword or a crossbow as its primary weapons?
Well now I understand everything you are doing. Really the only thing I think I would change is to allow the mech to use feats and shields. I think allowing those things would help with more player build options.
RAW: Feats and abilities which affect the pilot's attacks (such as great weapon master) do not affect the mech's attacks. The pilot is spending their action to command the mech to make the attack, and thus it does not count as the pilot's attack. Any rule which affects your attack or when you take the Attack action does not apply when you command the mech to make an attack.
Additionally, note that the mech gets to take an ASI when you reach relevant levels. But the mech must take and ASI and is not able to take a feat instead, even if you are using the optional rules for feats in your campaign.
If you want to take the Great Weapon Master feat (or another feat) and gain its benefits while attacking using the mech, I think an appropriate house rule would be as follows: When you reach 4th, 8th, 12th, 16th, or 19th level in this class you can forgo the mech's ASI in order for it to gain a feat which you currently possess (if you gain a feat at the same time, it counts as being currently possessed by you). The mech gains the benefits of this feat irrespective of whether it is being piloted or who it is being piloted by. The mech can gain the benefits of a feat which requires a weapon proficiency provided you possess that proficiency. The mech cannot take a feat which requires a prerequisite it lacks such as being a member of a certain race or the ability to cast a spell. If the feat grants an option which can modify an attack, such as Great Weapon Master and Sharpshooter, the pilot chooses whether to utilise that option when they command the mech to make an attack. If your mech makes an opportunity attack when it does not have a pilot, it does not utilise options such as those granted by Great Weapon Master and Sharpshooter.
Does that make sense and sound appropriate to you? I think it would be good to allow the Archanomechanist the option of taking feats. The way it is currently written, there is obviously there is no point taking feats which affect your attack when you'll be making all your attacks via the mech. But for balance purposes, this should come at the cost of both your ASI and the mech's ASI. We will get into why the mech is taking ASIs at all in the next section with regards to your second question.
Yes, I consulted the details for Beast Master Ranger, including the new Ranger Companion Options in the Class Feature Variants UA. The initial basis for the mech and its mechanics (as I think is very apparent) was the Battle Smith Artificer subclass and its [Tooltip Not Found], and Might of the Master was initially cribbed from there. But I needed to rework it a bit.
The Steel Defender's Might of the Master feature reads as follows, and the [Tooltip Not Found]'s Might of the Master feature works similarly.
Whereas the Archanomecha's Might of the Master feature reads as follows.
This is the same, except that I've removed the increase to hit and damage of the attack, as that is covered directly in the Primary Armed Strike etc action descriptions since these are affected by the pilot's proficiency modifier not the creator's. I've also had to add in a section which grants the archanomecha an ASI whenever the creator receives an ASI in this class. A battle smith can use their Intelligence modifier to make their weapon attacks (provided they use a magical weapon, but with artificer infusions any weapon can be magical for the day). For an archanomechanist, we want the mech to provide the strength for the attacks (this is a core aspect of the subclass). As the character advances in level, their attacks need to get stronger and for the archanomechanist, that means their mech needs to get stronger. It is not sufficient to have buffs tracking the proficiency modifier, since that would fall behind the battle smith (which can increase their Int to increase attack damage) or str/dex based martial classes which have buffs to their core stat as well as to their proficiency. I could have hard-coded increases to the mech's Strength ability score as the character levels up, but I wanted to provide the option for a Dexterity-based crossbow wielding mech. So instead I opted to give the mech its own ASI, which allows you to increase either its Str or Dex as your character progresses. After maxing the mech's attack stat, you can increase its weaker stats such as Dex, Int or Cha, or boost Con for a small HP increase. Unfortunately, the ASI changes to the mech can't be tracked in dndbeyond and must be managed elsewhere.
In addition to proficiency modifier buffs to attacks, saves, and skills (present in Might of the Master), the Best Master's companion also gains a buff to its AC. Note that the Beast of the Air and Beast of the Earth in the Class Feature Variants UA have a base AC of 13 and 12 respectively, so at 3rd level that's an AC of 15 or 14. That's (not coincidentally) the same as the Archanomecha's past/prospective and current baseline AC values, and if you take the Reinforced Plating design you'll have the same proficiency modifier-tracking AC progression as the Beast Master's companion. I decided to make this AC progression optional because I thought it would be too much to two designs at 5th level on top of this. I think it is better to have the number of designs granted consistent (two each time) and this way it is more flexible for the player.
The Beast Master's companion doesn't gain the benefits of ASI, and so falls behind in usefulness as the character progresses, unlike with the Archanomecha. This would have been even more of an issue for the Archanomecha because all your attacks are going to be channelled through it. One of the main complaints about the Beast Master is that it requires your attack to have the companion attack, yet the strength of the companion's attack falls behind as your character advances in level.
The Beast Master gets Hit Dice, for regaining hit points on a short rest. We instead follow the example set for the Steel Defender and Homunculus Servant. On a short rest, you can repeatedly cast the mending cantrip to restore your archanomecha to full health, so there is no need for it to have hit dice. Though it would probably be more balanced if it had to use Hit Dice, I decided to follow the example used in the rest of the artificer class.
RAW: No, the mech cannot wield a shield, only weapons. I did not want to add more complexity to cover this, but the rules could be rewritten to make wielding a shield permissible without too much difficulty. Amendments would be as follows:
Either the primary or secondary arm can wield a shield. The mech cannot attack using a arm which is wielding a shield. Wielding a shield grants a +2 bonus to the mech's AC. The mech only gains this bonus once, even if it bears a shield in more than one arm. When the mech wields a shield, the pilot's AC remains unchanged.
So if the shield is in the primary arm, you can't spend your action to attack with the primary arm. But you can spend your action to make an unarmed strike with the secondary arm. And you can use your bonus action to make an attack with the secondary arm as normal.
Similarly, if the shield is in the secondary arm, you can't spend your bonus action to attack with the secondary arm. But you can spend your bonus action to make an unarmed strike with the primary arm. And you can use your action to make an attack with the primary arm as normal.
I hope that helps. Let me know if you have any other questions or suggestions!
Oh one more question can the mech carry a shield?