Path of the Enhanced Being

While many barbarians' rage comes from their feral instincts, some brave alchemists have tried to harness it into a substance form. These artisans work tirelessly on refining this formula to make it safe, effective, and useful for all backgrounds. However, this is still experimental in nature, and overuse can severely damage one's body without a highly disciplined lifestyle.

Alchemical Knowledge

Upon taking this subclass, you gain proficiency in the alchemist's supplies if you don't already have it.

Enhancement Serum

With your alchemical knowledge, you can create an enhancement serum that induces your rage. This serum costs 25 gp per vial in materials, and you must have alchemist's supplies on hand to synthesize the serum.

Whenever you (or any other creature with this feature) rage, you can choose to induce it through an enhancement serum. By doing so, you gain advantage on all Constitution checks and saving throws. In addition, you gain advantages on saves against being frightened, charmed, or stunned.

Overdosing
If you have used all your rages between long rests, you can still try to induce a rage through the serum if you have spare vials of it through an overdose. Any saving throw involving you (or any creature with this feature) using this serum has a DC of 25-proficiency bonus-INT modifier-WIS modifier. To succeed in an overdose, you must succeed a Constitution saving throw. Upon success, the rage goes off as normal. However, subsequent attempts to overdose will increase the DC by 5 per each attempt. Upon failure on this save, the rage fails, and you take a level in exhaustion. In addition, if you have not taken a long rest since failing this save, you automatically fail all subsequent attempts at overdosing on the serum until you take a long rest.

Overdosing on this serum can have severe effects on your mind and sanity. After a rage induced by an overdose ends, you must roll a Charisma saving throw or suffer psychic damage equal to a number of d6 equal to your level.

Other Creatures Using the Serum
Other creatures without this feature can attempt to ingest the enhancement serum. For them, any saving throw involving this serum has a DC of 25-INT modifier-WIS modifier. These creatures must succeed on a Constitution saving throw. On a failed save, the creature suffers none of the effects of the serum and takes a level in exhaustion. After a successful save, they gain all the benefits of a normal rage (i.e., without the benefits of rage obtained with this class feature), but also have disadvantage on all intelligence, wisdom, and charisma saving throws. In addition, once the rage wears off, the user must roll a Charisma saving throw or suffer psychic damage equal to a number of d6 equal to their level. Creatures will automatically fail this save if they have not taken a long rest since the last successful save.

Artificial Antidote

At 6th level, your body becomes more accustomed to artificial chemicals in your bloodstream. When you induce a rage through the enhancement serum, you are immune to being poisoned and have resistance to all acid and poison damage. 

If you are poisoned before inducing a rage through the enhancement serum, all effects of that poison are completely halted during your rage and do not return after your rage ends.

Refined Process

At 10th level, the process of synthesizing the serum has become more efficient. Synthesizing the serum only takes 15 gp in materials, but you still must provide the alchemist's supplies.

In addition, the more efficient and refined process of creating the serum has reduced some of its adverse effects. Whenever you attempt and succeed in overusing the serum past your daily rages, a failed Wisdom saving throw only deals psychic damage equal to a number of d6 equal to half of your level (rounded down). Creatures who do not have this class feature still take the full level times d6 psychic damage on a failed Wisdom save.

Tenacity Through Tolerance

At 14th level, your body's tolerance of the enhancement serum can energize you in dire circumstances. Whenever you have induced a rage through the enhancement serum and are hit with an attack that would reduce you to 0 hit points, you can instead hang on with 1. When you use your reaction to make an opportunity attack between then and your next turn, that hit automatically becomes a critical hit. You can use this feature as many times as your constitution modifier (minimum of one) per long rest.