Eldritch Potion

Appearance:

An ominous swirling purple fluid in a sealed glass container. The fluid is never still, always moving inside its container. The scent is uniquely unsettling, not so much bad or disgusting, but unsettling. How does that make sense? When you walk past a trash can, and for some reason it smells good, or finding a beautiful flower and its fragrance is revolting. The aspect is the dissonance.

Effect:

An eldritch potion increases the consumer's spellcasting ability, making their spells stronger and increasing the number of spells they can cast. This is a temporary effect, and consuming more than one potion doesn't increase the potency, only extends the duration. Differing levels of quality can strongly effect the potency of the effect.

Side Effects:

Eldritch potions are not natural, and the longer and more consistently someone consumes them, the more the potions start to mark them.

The shorthand version would be that the more potions a being consumes, the more they will turn into Vincent Price.

Creation:

Brewing Eldritch Potions is more difficult than making Health or Mana potions, and requires the creator to be a master alchemist, master potion crafter, and be a sorcerer or warlock capable of casting the spell Eldritch Blast.

Czourvrash Glinrida of Krakenport is known to produce a small number of eldritch potions for sale, generally, these are spoken for before she even makes them. She is a cruel and unpleasant woman, charges exorbitant prices for said potions, and will only sell them to customers who have done a few bullshit fetch quests for her.

Beans Solagar of Terrasquestone is known for being a shady dealer of potions, tonics, and tinctures, and he has a ready supply of eldritch potions. These are of low quality, and he typically uses them to razzle-dazzle up cheap bottles of low-quality, high-proof booze.

Legend claims that the Ancient One Tarasqops, a leviathan with the seeming of a body of a whale, wings of an swan, legs of titan, and an insane-biological tri-form jaw filled with literally millions of needle teeth leaks eldritch potion of divine quality from it's ... cloaca?

Most dungeons are capable of synthesizing eldritch potions, but almost none do, other than Goblin aspected dungeons. In these dungeons, the goblin dungeon mages are always equipped with goblin gourds filled with eldritch potion.