Eret Si'Nu, Vapor form

The very foundation of magic is predicated on the usage of the mysterious energy source known as Eret Si'Nu or The Potential.
Ever since the coming of Mount Celene, Eret Si'Nu has been infused in the atmosphere of the entire world, having been initially emitted by the holy mountain itself. Whether it was released in massive quantities or if it somehow maintains the innate ability to replicate itself (this is still being studied by such luminaries as The Boorka), the "substance" has spread wide, covering the entire globe.
All magic, even divine in nature, utilizes Eret Si'Nu to function properly. It is the fuel that perpetuates both miracles and household magic. Some even believe the invisible molecules to possess an alien form of intelligence; one that decodes incantations and spell ingredients into the manifestations of arcane will desired by the caster.
As alluded to previously, Eret Si'Nu in most cases is entirely invisible and undetectable, even through magical means. It took some time and convincing the get the magical community to even believe in its existence (and believe me, there are still some significant hold outs on that front). That being said, there are a few cases (and places) where this veritable "mana from the heavens" exists in a gaseous form...
In the southlands of Hariel Minuta, typically in The Wastes of Veric, a few "vapor mines" have cropped up over the last few centuries. Desert tribes and nomads somehow discovered deposits of Eret Si'Nu in the badlands, where it is belched from the earth in a green vapor form. This super heated gas is extremely difficult to harvest, but once captured, it can be converted into a super-charged burst of hyper magical energy.
Vapor farms produce an amount of catchable gas (most of the gas evades capture in the mining process, possibly through intelligent evasion) the equivalent of somewhere between 50-100 cubic feet per day. Most mines are temporary in nature, and somewhat unstable. It's never known when one might pop up or shut down at any given time. As such, vapor farming is an extremely volatile industry (not helped by the fact that vapor miners have an overtly high mortality rate - as being caught in a vapor stream over an active vent produces enough heat to essentially melt skin and bone).
In game terms, the usage of Eret Si'Nu in gaseous form can both enhance spell casting strength (expressed in an increase of the effective level of a spell being cast) and/or help the caster retain their ability to continue casting more spells (expressed as the retention of expended spell slots). The Eret Si'Nu must be inhaled by the user, presumably after being allowed to cool.

Game Effects

One cubic inch of the vapor can be used for one of the following in-game effects.
1. For each cubic inch of vapor inhaled, a spell slot of the corresponding amount (level) may be retained. In other words, the spell would be cast, but the slot would remain unspent. For example, a mage would need to inhale nine cubic inches of Eret Si'Nu in order to retain a ninth-level spell slot. One cubic inch would thusly retain a first-level slot. And so on...
Note: One cannot gain or maintain a spell slot of a level for which the caster is not currently qualified.
2. Each cubic inch of vapor inhaled may alternatively be used to increase the power (as expressed in slot level used) of a given spell on a one-to-one ratio. In other words, if a mage desired to cast Magic Missile as a third-level spell (with the power of a third-level slot) but only wished to expend a first-level slot, 3 cubic inches of Eret Si'Nu must be inhaled.
Note: One cannot "level up" a spell beyond the maximum level of spell slot to which they normally have access.

Side Effects

The continual usage of Eret Si'nu is both an expensive and a quite dangerous habit. One cubic inch of Eret Si'Nu averages anywhere between 15-40 gold pieces in cost.
Further, after every use, the caster must make a CON saving throw to avoid addiction. The save begins low, with a DC of 8 for a single inhalation of 1 cubic inch, but increases by 1 for every inhalation of additional cubic inches. Even on the first attempt. So, a mage with access to 6th level spells inhales 6 cubic inches of Eret Si'Nu to retain their (spent) spell slot after casting. They must then make a CON save at DC 13 (the 1st cubic inch begins at DC8 and rises with each additional inch).
On a failed save, several things happen. The subject suddenly feels an extreme need to acquire more vapor, even at the expense of other necessities requiring funds. This need continues until their next inhalation (which commences a new CON save with an initial DC picking up where the last save left off), or until 2d6 days (minus their CON bonus) have passed. After the necessary time has elapsed, or if they succeed at their save at any time, the subject is freed of their temporary addiction. However, each time a save is failed, it adds 1d6 additionally to the amount of detox rehabilitation time.
The other, more insidious side effect is that until one of the end conditions previously mentioned is met (either detox time or a new dose with a successful save), all spells cast by the subject cost twice their spell slots. If the caster only has a maximum of one spell slot of a particular higher level, the additional cost will be the numerically equivalent number of lesser slots that would add up to the level of the one that cannot be met. In other words, if a character only has one ninth level slot and is currently suffering from Eret Si'Nu withdrawal, they could still cast a 9th level spell. However the cost would be that 9th level slot plus any combination of lower level slots that add up to nine (such as an 8th level slot and a 1st level slot).