Path of Duality

You are a being of two mentalities, but they need not compete against each other.  Perhaps each can help the other?

A Path of Duality barbarian gains the ability to cast spells, but still cannot do so while raging.  To compensate for this, they find ways of stealing magic from the environment, being able to do so while in a rage, and restoring spell slots.  Conversely, excess magic from their spellcasting gets channeled into shoring up their health, making said conversion when they enter a rage.

Spellcasting

You are a barbarian, made for battle, but have come upon primordial magics that you can shape to your will, channeled through your body from the very universe itself, and now seek to balance that magic.

Cantrips

You learn two cantrips of your choice from the sorcerer  spell list.  You learn an additional sorcerer cantrip of your choice at 10th level.

Spell Slots

The Spellcasting table shows how many spell slots you have to cast your spells of 1st level and higher.  To cast one of these spells, you must expend a slot of the spell’s level or higher. You regain all expended spell slots when you finish a long rest.

For example, if you know the 1st-level spell shield and have a 1st-level and a 2nd-level spell slot available, you can cast shield using either slot.

Spells Known of 1st-Level and Higher

You know three 1st-level Sorcerer spells of your choice.

The Spells Known column of the Path of Duality Spellcasting table shows when you learn more sorcerer spells of 1st level or higher.

Whenever you gain a level in this class, you can replace one of the sorcerer spells you know with another spell of your choice from the sorcerer spell list.  The new spell must be of a level for which you have spell slots.

Spellcasting Ability

Constitution is your spellcasting ability for your spells, since you're using primordial magic that's channeled from the universe and through your body.  You use your Constitution whenever a spell refers to your spellcasting ability.  In addition, you use your Constitution modifier when setting the saving throw DC for a spell you cast and when making an attack roll with one.

Spell save DC = 8 + your proficiency bonus + your Constitution modifier

Spell attack modifier = your proficiency bonus + your Constitution modifier 

Path of Duality Spellcasting

Barbarian Level	Cantrips Known	Spells Known	— Spell Slots per Spell Level —
			1st	2nd	3rd	4th
3rd	2	3	2	—	—	—
4th	2	4	3	—	—	—
5th	2	4	3	—	—	—
6th	2	4	3	—	—	—
7th	2	5	4	2	—	—
8th	2	6	4	2	—	—
9th	2	6	4	2	—	—
10th	3	7	4	3	—	—
11th	3	8	4	3	—	—
12th	3	8	4	3	—	—
13th	3	9	4	3	2	—
14th	3	10	4	3	2	—
15th	3	10	4	3	2	—
16th	3	11	4	3	3	—
17th	3	11	4	3	3	—
18th	3	11	4	3	3	—
19th	3	12	4	3	3	1
20th	3	13	4	3	3	1

Connected Duality

From 3rd level onward, your rage and your spell slots share a connection.

If the first thing you do after rolling initiative is going into a rage, then your lowest level expended spell slot is restored.

Additionally, for each spell slot you expend via casting before you go into a rage, you gain temporary hit points equal to your Constitution modifier, minimum 1 each.

Goodberry

From 3rd level onward, you know this spell.  It can be cast once without using a spell slot, and cannot be cast this way again until you finish a short or long rest.  It can also be cast using any spell slots you have.

Additionally, your healing spells have their healing improved by your proficiency bonus plus their spell level.

Strengthened Connection

From 6th level onward, the connection between your rage and your spell slots gets stronger.

For every critical hit or killing blow you land while raging, an expended spell slot of your choice is restored.

Additionally, your focus is honed enough that you can now maintain concentration on spells while raging, but still cannot cast additional spells while raging.

Superior Connection

From 10th level onward, your connection between magic and rage has strengthened to the point making you extra formidable in both.

Whenever an enemy misses on an attack roll against you, and the roll on their die is less than your Constitution modifier, your lowest level expended spell slot is restored.

Additionally, the temporary hit points you gain from casting spells using spell slots and then raging, is now multiplied by the level of the spell, rather than just being a flat amount.  For example, using a 2nd level spell slot will grant twice your Constitution modifier in temporary hit points the next time you rage.  Minimum is equal to the spell's level.

Regenerative Spell Slots

From level 10 onward, your ability to recover spell slots gets easier.

Whenever you take a short rest, you regain spell slots of your choice whose total levels do not exceed your Constitution modifier.

Perfect Balance

From level 14 onward, your connection between your magic and rage has been perfected.

Landing any non-critical hit on a foe, that isn't a killing blow, while raging, will now contribute towards restoring expended spell slots, with the number of hits required for each spell slot being equal to its level.  In order for it to contribute to a spell slot whose level is higher than 1, you must announce which level of spell slot you're working on when you land the first strike, it's then assumed that each qualifying strike after is contributing to that spell slot level.

Additionally, when you enter a rage, the temporary hit points gained from casting spells using spell slots also restores an equal amount of health.

Improved Regenerative Spell Slots

From level 14 onward, you have the ability to restore spell slots outside of resting conditions.

Whenever you have no spell slots remaining, you can use a bonus action to restore spell slots.  When you do so, expend a Hit Die and roll it.  Choose which spell slots you restore, keeping in mind that the total level of the restored spell slots must be equal to or less than the number rolled on the die.  If you roll a 12 on the die, you additionally create a temporary spell slot whose level is 1 higher than your highest level spell slot. This extra spell slot cannot be restored by any Path of Duality features.

Additionally, whenever you use this feature, you restore hit points equal to your Constitution modifier.  If your modifier is negative, count the hit point loss as psychic damage.