Equestria Vice

On PonyMUSH, we tack a fine line between family-friendly and Fear and Loathing, and nowhere is that line more blurry than in the Stuff Pirates Might Have in Their Cargo Holds department. While anything recognizable as a duplicate of an earthly illegal drug is probably off limits (and boring besides!), that doesn't stop us from imagining a wide variety of bizarre and magical vices, from potions to beverages and artifacts.

The following beverages, substances, items and potions may be varying degrees of illegal in Equestria with varying degrees of actual enforcement muscle, especially in Horseshoe Harbor, for reasons which should be fairly obvious.

There are more griffon poachers than pony poachers (although they certainly exist, and some accounts accuse the author of the Daring Do series of basing the titular character on one such poacher). Among valuable animal items might be:

Phoenix Eggs: Do we really need to explain why these are potentially a problem?
Dragon Scales: The older the dragon the better, and the less likely you are to get away without losing a limb.
Diamond Crabs: Vicious, highly dangerous, but the right buyer (say, a dragon) will give you a heaping fistful of his hoard for one.

Additionally you've got your various magical booze:

Bubble Beer: one of the more mundane varieties of magical lager, Bubble Beer is brewed from hops which have had their growth artificially induced by unicorn magic. The magic lingers in the hops through brewing and causes the beer's foaminess to stick around a surprisingly long time. Drinkers tend to hiccup large bubbles for several minutes.
Fireberry Wine: made from ripe fireberries, which only grow near volcanoes, does this weird burny-cooling thing to your throat and also grants temporary fire protection, banned in Equestria due to an extreme aphrodisiac effect on pegasi. (no other races are affected, cause unknown)
Slickwick: secret recipe of certain sages in the Gryphon kingdom, it's a sort of thick liqueur with the consistency of Bailey's and the color of absinthe. (Absinthe doesn't usually glow however.) Messes with your perception of time in ways sufficiently severe that Celestia has its sale tightly controlled, although not outright banned.
Eigenberry Wine: causes a temporary intelligence-enhancing effect, banned in Equestria due to various alarming side effects including dizziness, eye crossing, and general clumsiness.
Lokidraght: also known as "lie serum," Lokidraught induces compulsive lying. Fun at parties, as long as one doesn't, say, secretly spike the punch in a party full of already-angsty foals with it…
Rebos Stout: a rare brew with the curious property of absorbing alcohol in the body. Rare not because of it's difficulty in brewing but because who in Equestria wants a drink that makes them LESS drunk as the night goes on? Not, under any circumstances, to be taken as the first beer of the night.
Rainbow Extracts: Rainbow extract itself isn't in any way illegal, for similar reasons that spinning around in place isn't illegal: it's mostly unpleasant and impossible to regulate. But certain potionmasters can split out the chromatic essences into their pure forms, which is where the trouble starts…
Firefly Ale: Firefly Ale is not, in fact, made from any part of a firefly but is actually the result of heavily-treated extracts from the green area of the Rainbow, fermented under near-boiling conditions. It is so called because of the curious luminescence Zebras have been known to produce after drinking large quantities. The effects of large quantities of Firefly Ale on Ponies are not well studied, as Ponies experience much stronger bitterness in the beverage than Zebras. (It may be helpful to compare Zebra thoughts on this relationship to fans of certain ales.)
Red Lightning: The red area of the rainbow is the easiest to distill, but it's also a mostly flavorless fluid which tastes vaguely of sulfur— unless you then do something nopony is really sure how it was thought up: mount it to a lightning rod and get a few good blasts through it. The resultant shimmering red liquid burns the tongue, causes the drinker to build up a static charge that can straighten dreadlocks, and has an aphrodisiac effect that wears off at the moment of physical contact. (It has been established by experiments you do not want to know about that this isn't caused by getting shocked.)
Treason: Treason is so named because it looks and tastes exactly like orange juice but leaves a toxic aftertaste that lasts for days. On the Illegal or just frowned upon scale, this one is "probably".
SeaSpray's Folly: Another reason not to distill rainbow extract unless you absolutely know what you're doing is SeaSpray's Folly. Formed when anything but utmost care is used when distilling the orange section of the spectrum, SeaSpray's folly is a thick, viscous orange liquid which seems to be minimally sentient and extremely hostile to most of pony kind. Can be dispersed with water, but there are rumors of vast gyres of the stuff forming on the open sea….
Ultraviolet Potion: The most difficult to distill of the rainbow extracts, and the most prized. High pressures, low temperatures, and mirrors of varying sizes are all required. The secrets surrounding this potion are many, and given its effects are like a kind of positive-acting poison joke (amplifying a usually-weak aspect of the drinker to hyperbolic levels) those secrets are often jealously guarded.

Brewed Gemstones: because Equestrian gems experience a "life cycle" which includes a soft, fruitlike phase, they can be juiced to produce various healing elixirs. Of course, the real trouble starts once some fool Griffon builds a distillery on top of a gem mine and gets fermentation involved.
Diamond Ale: The buzz lasts for days, the hangover, WEEKS.
Emerald Liqueur: Otherwise known as Community Destroyer in a Bottle, Emerald Liqueur is a love poison with a twist: it acts not on present line of sight but on a 57-hour time delay, effectively randomizing the effect. For obvious reasons, this stuff is quite solidly illegal in most places.
Hematite Nightmare: It presumably took some serious lack of self-preservation to discover this, given how closely it resembles straight-up mercury, but if you ignore the extreme caffeine-like effects, affinity for heights and a hangover that makes you want to crawl under a rock and quietly wish every creature that makes noise would quietly dissolve, it's quite nice. Tastes sort of heavy and chocolatey.
Amethyst Cider: Not so much illegal as ludicrously expensive due to the six-thousand-step distillation process, which can take generations to complete. It's ambrosically delicious, carries a pleasant buzz, and nobody has ever been able to afford enough to get hung over. *Editors note to Salty: DO NOT TRY*

Poison Joke: Pretty much no matter how you ingest, inhale, or otherwise absorb Poison Joke, the results are the same: unpredictable physical side effects, usually of an ironic nature. Mostly unknown in Equestria, it's actually a popular prank substance in the Zebra territories, since the remedy is not difficult to brew. *Additional note:* Because Poison Joke often repeats its effects many or even every time for an individual, some ponies may develop a fondness for or even dependency on the herb.

Blurdots: Small mint-like objects which grant the user super-equine speed, with only a slight impairment to fine motor control. Fine motor control, on the other hand, can be pretty vital when you're going a mile a minute…

Timewine: Timewine is made by taking a flask of pure water, sealing it well, and then mounting it on a stick exposed to both the sun and the moon for a hundred years. It induces potent, vivid halucinations of the drinker's future, sometimes days, sometimes years ahead. Reports vary wildly as to the accuracy of these visions.

Puddleshrooms: Fungi native to the Wintersong Forest which have adapted to the intense cold of the deep woods by generating their own heat, so named for the pools of melted snow which accumulate around them. They act as a natural sedative and give their users what is described as a "warm fuzzy feeling" which can be highly addictive. Overdosing on puddleshrooms exhibits symptoms similar to heat stroke, which combined with the dangerously low temperatures of their native climate can be a one-two punch that can kill an unsuspecting pony who eats them for sustenance out in the wild.

Potions: Love, charm, fear, magic resistance, Moment of Terrifying Clarity In A Bottle, Rebound Relationship In 30 Seconds In A Bottle, etc…

And of course, good old fashioned forbidden artifacts of doom:
Flashgems: unknown origin, causes instantaneous teleportation to *seemingly* random locations far-flung, often plot convenient, when held to the light *just so*. Rumors of "destiny" swirl around these things like flies at a fruitbowl.
Spell Books: unicorn magic rarely *depends* on books, but a number of other magical traditions in Greater Equestria involve them. Trouble could arise should a novice attempt to use one…
Dreamstones: rare enough and obvious enough that a dreamstone is generally followed by several interested parties including the Equestrian Guard, dreamstones re-shape the world around a sleeper to match their dreams. In the hands of an experienced lucid dreamer, one of these could be incalculably dangerous…