The Arcane Theorist is a rarity among artificers. Blessed with the intellect and skill necessary for this unforgiving craft, the Arcane Theorist lacks the obsession with long-term projects innate to their kin. They make up for this in adaptability, plying their unique genius to unlock secrets others would find inaccessible. As their experiments and studies progress, they gain familiarity with nearly every spell in existence. While their knowledge may never reach full mastery, they can empower their spells to heights other artificers simply cannot reach. Left alone, an Arcane Theorist might derive from first principles the entirety of magical lore... though fate rarely grants them such an opportunity.

Tool Proficiency

When you adopt this specialization at 3rd level, you gain proficiency with calligrapher's supplies. If you already have this proficiency, you gain proficiency with one other type of artisan's tools of your choice.

Arcane Breakthroughs

Starting at 3rd level, you gain amazing insights into spell effects beyond the reach of most artificers. Choose one of the following classes: bard, cleric, druid, paladin, ranger, sorcerer, warlock, or wizard. This class’s spells become part of your Breakthrough spell list. You can choose an additional class and add its spells to your Breakthrough spell list at 5th, 9th, 13th, and 17th levels. You can cast (but not copy) spell scrolls containing spells on your Breakthrough spell list.

When you change your list of prepared artificer spells after a long rest, you can prepare an additional spell. This spell must be from your Breakthrough spell list, and must be of a level for which you have spell slots. When you reach certain levels in this class, you increase the number of Breakthrough spells that you can prepare. You can prepare a total of two Breakthrough spells at 5th level, three at 9th level, four at 13th level, and five at 17th level. These prepared spells don’t count against the number of artificer spells you prepare.

When you cast a spell you’ve prepared using this feature, it’s considered to be an artificer spell for you, and Intelligence is your spellcasting ability for it.

Bard Spells

You add the bard spell list to your Breakthrough spell list.

Cleric Spells

You add the cleric spell list to your Breakthrough spell list.

Druid Spells

You add the druid spell list to your Breakthrough spell list.

Paladin Spells

You add the Paladin spell list to your Breakthrough spell list.

Ranger Spells

You add the ranger spell list to your Breakthrough spell list.

Sorcerer Spells

You add the sorcerer spell list to your Breakthrough spell list.

Warlock Spells

You add the warlock spell list to your Breakthrough spell list.

Wizard Spells

You add the wizard spell list to your Breakthrough spell list.

Cantrip Specialist

You excel at producing minor magical effects - and at abandoning your current projects to pursue new ideas. Starting at 3rd level you gain the following benefits:

• You know one additional cantrip beyond what’s normally allowed for an artificer of your level.
• When you finish a short rest (instead of when you gain a level in this class), you can replace one of the artificer cantrips you know with another cantrip from the artificer spell list or your Breakthrough spell list. This cantrip is considered an artificer cantrip for you.

Cantrip Savant

Starting at 5th level, you continue to develop your talent for the simplest spells. You gain the following benefits:

• When casting an artificer cantrip, you gain a bonus to one roll of the spell. That roll must be a damage roll, and the bonus equals your Intelligence modifier (minimum of +1). 
• As an action, you can replace an artificer cantrip you know with a different cantrip from the artificer spell list or your Breakthrough spell list. Once you use this feature, you can’t use it again until you finish a long rest.

Fluid Concentration

Your focus is never fully in one place; if your concentration on one spell falters, you can shift it adeptly. At 5th level, you gain the following reaction:

• Flowing Focus: When you would make a saving throw to maintain concentration on a spell, you may instead take this reaction. The spell you are currently concentrating on ends, and you may cast a different spell, subject to the following restrictions:
  
  • The spell must have a different name than the spell you ended with this reaction.
  • The spell must have a casting time of 1 action or 1 bonus action. You cannot ritual cast a spell using this reaction.
  • The spell must require concentration.
  • The spell must have a base level less than or equal to the spell you ended with this reaction.

If the spell you cast using this reaction is one of your Breakthrough spells, then you may cast it without expending a spell slot at its base level. Otherwise, you cast the spell as usual. You can use this reaction a number of times equal to your proficiency bonus, and you regain all expended uses on a long rest.

Superior Breakthroughs

Starting at 9th level, when you cast one of the spells you prepared with Arcane Breakthroughs, you can do so as if the spell was cast using a spell slot one level higher than the spell slot you expend. At 15th level, you can do so as if the spell was cast using a spell slot two levels higher than the spell slot you expend.

You can use this feature a number of times equal to your Intelligence modifier (minimum of 1). You regain all expended uses after you finish a long rest.

Work in Progress

Starting at 9th level, you can ready half-formed projects for easy completion when needed. As an action, you can replace any prepared artificer spell with any other spell from the artificer spell list, which then counts as a prepared spell for you.

Once you use this feature, you can’t use it again until you finish a short or a long rest.

Furthermore, your multitasking abilities make it easier for you to craft spell scrolls. When you craft a spell scroll, you can work in 1-hour increments, rather than 8-hour increments. As per usual, you can work no more than 8 hours per day on a spell scroll. Additionally, this work is considered light activity for you, and can be done half as efficiently while traveling (meaning you must work for 2 hours to make 1 hour of progress).

Final Breakthrough

At 15th level, your grasp on the fundamental principles underlying all arcana is ironclad. You have one additional spell slot of each level for which you can prepare artificer spells. Additionally, when you use your Superior Breakthroughs ability to upcast a Breakthrough spell, you can now do so as if it were two levels higher than the slot you expend.