Very powerful at high levels. Pretty alright at low levels if power-gamed.
First of all this needs playtesting. Analyzing it is too complex to return reliable results. I will do my best but playtesting will give better feedback than I can give.
Artificers are bizarre and difficult to quantitatively balance.
They gain power in strange ways which makes them difficult to compare to other classes. As a regular class they are supported mainly by their ability to create powerful infusions. The issue is that this happens outside of combat so in combat it is unclear how exactly they will behave. In addition the infusions can be given to other players to increase their potency. They are a half-caster so they can cast some spells but they will rely on cantrips/weapons much more often than full casters and lack upgrades to weapon attacks like other half-casters.
The subclasses all have different approaches to completing the class:
- The Alchemist leans in to out of combat preparation. Their actions in combat will be less helpful but they can be a major boon in supporting the party ahead of time. They only become powerful once they have enough spell slots to freely make elixers. Before that they are fairly weak in combat and don't offer much out of combat.
- The Artillerist gives the Artificer a chance to truly shine in combat via the turret. The turret is limited in its use but if the Artillerist spaces out their spell casting it can effectively be used all day. The Artillerist is effective at damage dealing from level 3+ but does not offer the unique, non-concentration, buffs of the Alchemist.
- The Battle Smith makes the Artificer like other half-casters by giving them a regular attack that keeps up at higher levels. Its damage might be less than the Artillerist but it is less finicky and lets the Battlesmith shine as a melee attacker better.
I think your subclass takes an approach somewhere between the Battle Smith and the Artillerist. You grant ways to make your Artificer very power for short periods by making the spells extraordinarily formidable/difficult to disrupt. You grant ways to participate more regularly in combat by granting more spells and boosting cantrips. The best way to balance this class is to playtest it
Analysis by level
feel free to skip to the TLDR. This is my way of showing the power progression and how it can maximized.
- The big bonuses here are casting as a bonus action and concealing the effect of Charm.
- The latter is fairly situational and eats into your 3 daily spells.
- The former can only be used on Minor Illusion or possibly one of your 3 daily spells.
- The benefit to the daily spells is at most 1d10 fire damage from Firebolt. You would use a cantrip rather than a weapon because you will have at least one hand full of your instrument (no bow or crossbow) and will want to keep at range to maintain concentration.
- The benefit of Minor Illusion every round depends strongly on your DM. Some DMs will have a monster walk through a wall that mysteriously appears. Some will have the monster spend its action Investigating to reveal the illusion. I think the best, consistent, RAW benefit you can get is blocking line of sight between two creatures to prevent spells and opportunity attacks. This is pretty helpful but also can become repetitive. The effect of Minor Illusion practically every round needs playtesting with a variety of DMs and players to understand its impact.
- At this level I would skip an ASI and instead take Magical Initiate. I would take Friends, Vicious Mockery, and some 1st level Bard spell (Tasha's Hideous Laughter, Unearthly Chorus, and Heroism are all good options). This dramatically boosts the value of your 3rd level features.
- Because Enchantment spells won't make the target hostile Friends is now advantage on all Charisma checks. I would have picked up Persuasion proficiency from my background making up for less CHA. At this level permanent advantage makes up for lesser bonuses but at higher levels proficiency will make you good at Persuasion regardless of CHA.
- Because you can now cast Vicious Mockery as a bonus action you can do 1d10 from Firebolt + 1d4 from Vicious Mockery every round as well as cause disadvantage on an attack. This more than makes up for not having a damage modifier (like when using a weapon) Cantrips level so this will benefit will level as well.
- The additional 1st level spell will synchronize with later features and make the bonus action ability more useful. It will also help overcome your limited spells known and your limited spell slots.
- At this level you get a major boost. Disadvantage on saves is very powerful.
- Your spells are much more reliable and you have more spells. Using Tasha's Hideous Laughter, Phantasmal Force, Suggestion, Calm Emotions, or Silent Image I would expect you to reliably remove one or more enemies from combat in the first round of combat 4 times a day.
- Vicious Mockery increased in damage and saves will now be at disadvantage. The increased chance to hit combined with the de-buff effect makes casting Vicious Mockery a second time generally better than Firebolt. An average of 10 damage with a high chance of hitting and disadvantage on up to two enemy attacks is very good.
- through level 8. You just get standard Artificer Features. A number of aspects improve.
- You get access to level 6 infusions. I will only consider infusions that would synergize with the Arcane Luther's features.
- Make Eyes of Charming to cast Charm Person thrice per day. Even though the save DC will be low you can reliably cause it to be at disadvantage.
- The UA Spell-Refueling Ring would break this subclass and should not be allowed. Regaining spell-slots would overcome the core limiting factor of the sub-class.
- Increased spells means Disadvantage on saving throws becomes relevant more often.
- The ASI at level 8 will boost your Intelligence leading to Vicious Mockery being even more reliable. This reduces the cost of taking a feat but you are still behind other casters.
- Your feature here is powerful and you also get access to 3rd level spells.
- Fortunately spell-storing doesn't work with the other spell buffs so the subclass still has limited ability to break combat. If used by the Artificer this would allow more rounds casting spells, all of which would still have Vicious Mockery cast as a bonus action or even a different leveled spell. I would probably use it to support a different player or an NPC, however, because at this point the Arcane Luthier is doing alright on their total number of spells and can get fantastic regular utility out of Vicious Mockery, and will want to save concentration for casting Illusion/Enchantment spells. This would be especially useful to give to a ranged fighter/rogue because they have nothing else to concentrate on and are unlikely to be hit. Some options to use it
- Fill it with See Invisibility and use it to buff the whole party twice per day (assuming +4 INT and 4 PCs)
- Fill it with Hold Person and give it to a hired commoner. They can cast once or twice every combat and hide for the rest of the time. This can also be used to burn legendary resistances.
- Fill it with Shatter and have a line of hired commoners use it and pass it down the line. If they fail to save 50% of the time it will be an average of 80 DMG per target. This demonstrates how powerful the original Spell Storing Item can be but the Arcane Luthier gets it an additional time, earlier, and with arguably better spell options (Hold Person).
- 3rd level spells include Hypnotic Pattern. This is a game changer because you will be able to cause a large number of enemies to be rendered useless. The spell save DC is probably 16 (8 + 4 INT + 4 Prof) so even foes with +9 to Wisdom saves (+5 WIS +4 Prof) will fail more than half the time. Enemies without a bonus to Wisdom saves will fail 90% of the time. You could reasonably win a number of encounters in the very first round.
- You get more infusion options
- The winged boots don't really synergize with your class but they offer excellent utility in and out of combat. If combined with Cloak of Protection and Gloves of missile snaring you have a good way to avoid being anyone's target.
- The Hat of Disguise works with your spell buffs. Disguise self at will might be foiled a bit by your playing an instrument but could still be very useful.
- More spell storing and a boost to cantrips
- Vicious Mockery does more damage. If you cast it twice around 5 more damage.
- You get the regular Spell Storing Item. This doubles the power of the level 9 feature. With 16 hench-people and failing 50% of the time this could be 369 AoE damage during a single round. The battle becomes a game of trying to keep the enemies from grabbing the items as they get passed along. Of course a DM probably wouldn't let you do this every day. This is also a great chance for Unearthly Chorus to be used to get the support of a mob of townsfolk. I am not saying the spell storing item is overpowered just that it can be very powerful so granting it a second time should not be underestimated.
- ASI, you now have 20 INT.
- Proficiency bonus increase and 4th level spells.
- With the Proficiency Increase and ASI an enemy with 20 Wisdom and equal proficiency will fail against Hypnotic Pattern 57% of the time. Without disadvantage on the save that would be 35%.
- 4th level spells are great but they don't synergize very well with the class. You mostly get more options rather than more power.
- Confusion has an automatic 20% of having no effect (except to deny reactions) and allows repeated saves.
- Compulsion consumes your bonus action (which means less Vicious Mockery) and allows repeated saves.
- Greater Invisibility can be cast as a bonus action but prevents you from using Hypnotic Pattern and other concentration spells.
- Hallucinatory Terrain might be harder to save against if you are playing music but it is also more situational.
- Polymorph doesn't synergize but is good enough to deserve a mention considering the Arcane Luthier gets it from the Bard's spell list.
- More infusions none of which synergize particularly well although Dimensional Shackles might be good against a victim of Tasha's Hideous Laughter or Hypnotic Pattern
- A big boost to defence. This will mostly help you keep concentration.
- Disadvantage on attacking you will make you very difficult to hit, especially considering you might have AC 25 if you use all of your infusions to boost AC.
- Sanctuary gives you an even more powerful means of defence and not being able to attack or cast spells might be worth it if you are maintaining concentration on Hypnotic Pattern to keep half the enemies down.
- Mass Suggestion is a great spell for the class and it moves the Arcane Luthier even closer to being a full caster.
- and up You get various nice features and spells but honestly at this point balance goes out the window regardless.
TLDR: Disadvantage on saves is very powerful and can synergize with many other features. Before level 9 ish the Arcane Luthier is limited by limited spells. If they get access to Vicious Mockery, however, they will still be effective in combat. At high levels the Arcane Luthier can regularly end encounters when the circumstances are favorable. When they are unfavorable the Arcane Luthier still has plenty of decent and powerful options. The Arcane Luthier can, with a bit of planning, use spell storing items to unleash encounter breaking damage. This isn't unique to the Arcane Luthier but the Arcane Luthier can do so more easily, more powerfully, more often, and two levels earlier. Even without spell storing shenanigans the feature is quite powerful by allowing other PCs to concentrate on a spell.
The subclass will be weakest when:
- You are out of spell slots. This will become less likely as you gain levels but will remain a limiting factor until around level 9. At level 9 you will be able to cast a concentration spell at the start of every combat and still have additional slots available.
- You are facing monsters that cannot be charmed. This will become more likely as you gain levels. You will still have solid cantrip damage, however, and at higher levels you can keep a different spell on hand to help balance out the issue. Even without using your spell buffs you can be effective with double cast Vicious Mockery
- Your DM decides playing an instrument in not situationally appropriate or is impossible.
The subclass will dominate when:
- Enemies can be charmed and don't have very high Wisdom saves. The Arcane Luthier will incapacitate many of them right at the start and can disadvantage any that remain.
- You are faced with a social encounter. Constant advantage on Charisma checks is a big bonus regardless of level.
- You have many followers (levels 9+). The shenanigans that can be done with the Spell Storing Item are so severe that the nature of combat will be redefined.
The Arcane Luthier will keep up in regular combat just by having double Vicious Mockery. Vicious Mockery damage won't be the highest, only about 20 at level 17, but it will be very consistent, because of disadvantage on the saving throw, and be rarely resisted. Disadvantage on the first attack becomes less helpful at higher levels when monsters rely more on multi-attack. Since monster damage scales as well, however, it is still useful and probably will give decent damage reduction when applied to two enemies. Importantly it makes critical hits very rare.
When the Arcane Luthier chooses to spend spell slots the effect will be overwhelming unless the enemy is immune to charm and has Truesight. Phantasmal Force and Tasha's Hideous Laughter will both be easily available at higher levels and will consistently be able to disable targets.
The features of the Arcane Luthier synergize very well but make it so that the Arcane Luthier can be too powerful in some situations especially at higher levels. Some more diversity in the design would probably be good so that there is less synergy but greater ability to address different situations.
I think a good point of comparison would be the Warlock.
- Both function as half-casters that try to be full-casters
- Both have access to an array of unusual features (infusions and invocations)
- Both will get access to potent regular cantrip damage if they plan for it (by taking agonizing blast or taking Magic Initiate/Bard multiclassing)
- Both will have means to maximize the effect of limited spell slots (Warlocks by having more higher level slots, Arcane Luthiers by having very difficult saves)
Of the two I think the Arcane Luthier comes out ahead.
- Disabling is more effective than damaging
- Greater adaptability to new situations (significantly more options for spell preparation, can move the infusions around, and more spells prepared)
- Better action economy (bonus action Vicious Mockery while casting a spell) and so does better once spells stop being a restricting factor.
- Better infusion options than the warlock's invocation options. Even if the Warlock gets more total active invocations the options are less helpful, conflict with other actions (especially if it consumes a spell slot) and cannot be given to other creatures.
- The Arcane Luthier can cast ritual spells allowing for more out of combat utility.
- Better defense
- Better socially by having constant advantage on Charisma checks, more socially useful spells, more tool/instrument proficiencies (situational) and much better Knowledge checks.
Does this mean the subclass is unbalanced? Not necessarily. Part of the reason why debuffs and buffs are okay is that it helps the whole party do better. If the Arcane Luthier disables a foe and the fighter lands the finishing blow both characters have had a chance to shine. The unbalancing part comes when the Arcane Luthier uses Hypnotic Pattern and stops the whole combat. How much of an issue that will be depends on how many of the enemies are proficient at Wisdom saves and how many are immune to Charm. This is part of why playtesting is so important because the power of this ability is difficult to quantify.
- Give the option of a Illusion/Enchantment cantrip from the Bard list instead of specifically Minor Illusion. This way the ability to function is less DM dependent and the basic damage option is available without taking a feat. Having a basic damage option is important at low-levels if this class is going to depend on spellcasting more. Alternatively just include Vicious Mockery along with Minor Illusion. I think this class needs an effective basic damage option for levels 5-9. The other subclasses get one in one way or another.
- Ditch the buff to Charm with enchantment spells. It breaks the normal function of the Friends cantrip and the level 3 boost is already decent if you include Vicious Mockery. Better would be to throw in Performance proficiency.
- Revise Beguiling Melodies. You should limit the number of times per day that it can be used. I recommend that it can affect a single spell once per short rest. In addition the second part is basically useless and just adds complexity so I advise getting rid of it.
- Revise Battlefield Control. Ditch either the first or the second part and have the other apply. If you keep the first part lose the charm requirement. If you keep the second part lose the limit to uses. Instead have it take effect immediately after you use Beguiling Melodies. In addition increase the number of uses of Beguiling Melodies to twice per short rest. I think Mass Suggestion works well here.
Is this an Artificer?
The spellcasting is unlike that of other Artificers and copies the style of the bard
The artificer doesn't "appear to be casting spells in a conventional way; [they] look as if [they]’re producing wonders through various items."
How will the Arcane Luthier look when casting a spell? The Battle Smith doesn't cast Shield with arcane gestures but rather bangs their smith's hammer against a silvery orb that splits open to emit a shimmering forcefield. If the Arcane Luthier just plays the instrument then they will look just like a bard. How are they interacting with the weave? They can use any instrument that they are proficient with so it isn't that the instrument is magical. They are then manipulating the weave through a particular series of notes. That seems again very similar to what the bard is doing. The artificer is supposed to create magic through invention and that isn't how your subclass functions. This isn't a problem in that you can change lore freely and the aesthetics of a class are hardly set in stone. It does make your subclass very distinct from other artificers.