1. An Elemental Devil
Long ago an elemental devil was trapped in the lamp. Once released it appears as an ornate oni mask, wreathed in blue and green flames. Once released, the devil will interrogate the summoner about the state of the world, and once satisfied will either enslave them, burn them to ash, or offer to help them, depending on their alignment. The elemental devil takes great delight in leading the innocent to damnation, or immolating those who are just petty evil. If summoned by a skilled magus, the elemental devil can be tamed, and made into a powerful, if unwilling servant.
Tips: the Elemental Devil has a mocking laugh, enjoys taunting and tempting others, and should be as obnoxious as attending a karaoke contest between Gilbert Gottfried and Fran Drescher.
2. The Silent Ones
The lamp contains a large number of spectres. These are harmless shadow beings with luminous golden eyes. Once released from the lamp they will incessantly follow the summoner. While unable to harm the summoner, they will constantly distract them, wander about in their vicinity, and can only be seen by the summoner.
Tips: the silent ones should be unsettling, disrupt sleep, cause distractions, and so forth. They are pleased by the spilling of blood.
3. Inna Gada Da Vida
The vessel was the prison for a rogue chaos elemental, and when released it pours from the spout as a continuous stream of iridescent butterflies. This cloud is a single entity of alien intelligence, no determinate alignment, and has no interest or agenda. It is a constant source of chaotic magic and can be harnessed as a potent power source for chaos magic. This is neutral, so can fuel green life magics, wild pyrotechnics, mutation spells, and so forth.
Tips: half cat, and roll on a d1000 chaos magic random generator once per round of interaction.
The vessel was a prison for a monstrous slug like abomination. After it's long captivity it has duplicated itself an untold number of times, and now the lamp contains an unimaginable number of slitheroids of all different sizes. They emerge ravenous and full of sluggy eggs.
Tips: see the movie Slither
5. Demonic Genie
It looks like a genie, it talks like a genie, it grants wishes like a genie, but it bargains like a minion of the Abyss. Which it is. The demon has long played the role of a dark genie, granting wishes in exchange for souls, and making absolute monkey's paws out of every wish it grants. It is evil through and through and appeals to the summoner's based urges and desires.
Tips: see the movie Wishmaster
6. The Shade of Burning Fangs
Burning Fangs was a great and terrible dragon, and those who slew it became great heroes. Not to be outdone, Burning Fangs had access to dark magics and while not returning as a dracolich, it did manifest itself as a ghost. Becoming the Shade of Burning Fangs, the ghost ran roughshod over the lands it once terrorized until it was captured and put into the vessel and thrown down a deep and hopefully bottomless well. The lamp has been found and when released, the Shade of Burning Fangs will engage in a contest of wills, if it wins it is free, if it loses, it is the servant of the lamp holder.
Tips: It is the ghost of a vengeful and hateful dragon, breathes cold flame, and has access to necromantic magic
7. Phantom Aberration
The lamp is the prison of a phantom aberration. It appears as any suitable aberration (such as a giant neogi, umber hulk, catoblepas, etc) but rather than being solid, it is an energy ghost. Intangible, but luminescent, able to phase through walls, and it's touch has a lifestealing power. Once the phantom has gained enough power it will bulge, and a second aberration will erupt from the first, in a vile sort of mitosis.
Tips: Watch Final Fantasy: the Spirits Within
8. A swarm of insects
The lamp has a trap spell on it, and when activated, the lamp emits a cloud of biting and stinging insects to harry and harass the summoner and their party.
Tips: Summon Insect Swarm (level comparable to the PC who activated the lamp)
9. The Arcane Blasphemer
The lamp was used as a prison for Caegor the Arcane Blasphemer, an particularly unpleasant individual. Caegor was a centaur wizard who embraced the darkest of arts and made pacts with the star fallen to draw on powerful chaos magic in a bid to dominate the world and exterminate 90% of the sentient races. The Arcane Blasphemer could not be destroyed, but a powerful Wish spell was used to bind the Arcane Blasphemer into a magic lamp, ending his reign of unholy and alien terror. Once released, Caegor will challenge the summoner to a test of wills, and if he breaks free will begin rebuilding his forest temple to an outer god of desolation and madness and prepare to summon it.
10. A Faceless One
The Faceless Ones are a deep and ancient race of doppelgangers, and their true form is unknown but is suspected to be horror beyond imagination. They will mimic the appearance of the summoner, and after this will emulate other people, but always favoring the summoner. Rather than being horrific monsters, faceless ones are easily bored, and are tricksters at heart. Most are bound because they are a nuisance rather than a treat to humanity and sentient races. They can be spotted by the fact that the sclera of their eyes is a translucent black, rather than the normal white color.
11. A Gibbering Mouther
Instead of a stream of smoke, the lamp being spewing out a chunky stream of blood and viscera. The pool becomes elastic as it gushes out, until a particularly large gibbering mouther is before the summoner, all rolling eyes and obscene mouths. It speaks in a dozen voices in a dozen languages, and is unspeakably insane and alien in nature. If the summoner loses the contest of wills, the mouther will eat them. If they win, they have the services of a bottomless maw full of blasphemies and obscenities
12. The Great Ungez Queen Imago
Great Ungez, magic using giant cockroaches are already horrific, but the entity that calls itself Imago is an especially large and intelligent great ungez, being human sized in her normal form. She is also a potent sorceress and specializes in charms, wardings, holding spells, and commonly copying the appearance of women she considers beautiful. She cannot completely conceal her evil ungez nature and is accordingly callous and cruel, and also completely immune to poison, filth, and shock. If uncontrolled she will seek mates and begin breeding, creating hordes of mundane great ungez to infest the location.
13. The Fractal Queen
The Fractal Queen is an energy being aligned with chaos and corruption. It appears as a geometric patterned shadow that is constantly changing shape like it is in a kaleidoscope. Technically an eldritch being and outer god, the Fractal Queen is obsessed with humans and elves, particularly attractive men. To feed this desire, the Queen will corrupt and spiritually dominate a cadre of women and androgynous men to serve her in her game of seduction. The lamp holder and summoner is just the first obstacle the Queen must overcome, unless the summoner is a handsome man of action and magical power and then there is a chance the queen will willingly serve him.
14. A Corrupted Elemental
Elementals can fall, be contaminated and corrupted. Destroying such a primal force can be difficult, so imprisonment is often a saer answer, since corruption can be spread like a disease among other elementals of the same type. Corruption can include fae (alignment becomes chaotic, appearance becomes polychromatic) infernal (alignment to evil, appearance becomes demonic) Eldritch (alignment chaotic evil, appearance Lovecraftian) underworld (element added, entropy, appeance becomes zombie-like and decayed) celestial (alignment to lawful, appearance becomes angelic). These beings are powerful and dangerous.
15. A Giant Ghost Head
The Lamp is a trap and contains a gigaschel, an artificial type of ghost. The gigaschadel will pursue the summoner first and then seek to destroy the rest of the summoners party if able, and will then return to its creator, or the lamp if it undamaged.
16. A Necrogenic Cloud
The lamp produces a thick damp cloud of roiling green smoke, necrogen. Any corpses in the vicinity quickly rise as undead, and the injured must make health checks or begin taking damage from the necrogen attacking their life force. Not intended as a trap, the lamp is an ornate necromancer's Create Undead grenade.
The Lamp contains a mundane animal, but it is dramatically larger than it should be, and if controlled it will serve the summoner, if not, it will attack. It cannot flee so long as the summoner remains alive and holding the lamp. The animal is magical in nature, and injuries are healed by being returned to the lamp, and it need not eat. Medium (normal size) animals are large enough to ride like a horse, small animals are the size of large wolves. Large animals like horses, moose, etc, are huge. Paul Bunyan's blue ox Babe would be a good example.
18. Kotzengran the Siege Engine
Kotzengran the Siege Engine is a war god, and appears as a twelve foot tall stylized representation of a orc or ogre. Kotzengran is clad in animalistic ceremonial armor, and carried no weapons. He is a servant of a long vanished magical monarchy and in battle can emulate the function of three different siege weapons. He can hurl a giant spear like a ballista, can throw boulders like a catapult, and against fortifications and walls, he can deliver a shoulder blow like a battering ram. The Siege Engine will willingly serve those of noble blood, or noble sorcerous blood. It will not serve those who are chaotic in nature, and those of common origin must master Kotzengran in a contest of wills otherwise it will not serve them.
19. Eizzal the Mimic-Master
Eizzal the Mimic-Master began life as a normal dungeon mimic (the creature) but was caught up in a failed Contingency spell. The spell fused the mimic with a now forgotten Adventurer-Upon-Return, creating a humanoid sorcerer mimic. Eizzal devoured the other mimics, and then the rest of the denizens of the dungeon and replaced them with her spawn. These new mimics were twice the normal size, and almost all had rudimentary magical ability. Rather than slaying Eizzal, some questionable magi captured her, trapped her in a lamp, and forgot about her on a shelf until she was lost and became another piece of loot. Eizzal is not and was never human, has moderate magical power, and can act as a doppelganger and a mimic. If she mates, she can lay mimic eggs. If she eats a massive amount of biomass, she can cleave off parts of her body to make mini-mimics that will grow. She is quite sane and reasonable, mimics have a massive amount of patience and not much motivation.
20. Yazoin, the Executioner
Yazoin the Executioner was a female half-giant feared and reknowned for her prowess with a great axe. After crossing the line one too many times, Yazoin was imprisoned and made the head executioner for a dark kingdom. In this role she would appear wearing a great belt and iron shod boots, and an enormous steel helmet. This was terrifying for those about to be decapitated, thrilling for the audience, and a form of punishment for Yazoin. Her topless appearance was just more shock value. The King refused to let his prize go, so he tasked his magi with binding Yazoin into a summoning device so that she would always be available. The kingdom fell, the half-giant tribe was hunted to the last, and even most of her language is forgotten. Yazoin remains a prisoner, and must serve the holder of the lamp, though her hatred is enormous. Should she ever break free of this control, she would go on a murderous rampage even the gods would be forced to take notice.
21. Swarm of Alkonosts
An alkonost is a large but otherwise unremarkable bird that has the head of a human female. They speak and are intelligent, but are still first and foremost, avians. The first alkonosts were cursed by magic, having been human. Their offspring continued as a new species. It is a quirk of magic that all alkonost have female faces and voices, regardless of their actual gender, the original victims were all women. The lamp contains a number of alkonosts, who were infesting a specific location. Rather than kill the intelligent birds, they were placed in the lamp for 'safekeeping' and forgotten. The number inside the lamp is fixed, there are more than 20 inside. Each is an individual, and has a self identity, and interest. They can be conversed with but have short attention spans.
22. Azerrad the Deathless
Azerrad the Deathless is a vampire. An old school slavic vampire. Its natural form is a dense green-gray smoke that is slow moving and heavier than air. It can be induced to turn the freshly dead into mindless lesser vampires, who will rise and serve it. Azerrad was a cause of desolation in a mountainous region and caused much grief and many deaths among the heroic orders. Many tried to fight and kill it, but each time Azerrad demonstrated new abilities. It could turn into a monstrous man eating bat monster. It could turn into a cloud of bats. It could mesmerize the living. It could turn the living into mundane vampires. It was eventually defeated by being sucked into a magic lamp and then placed in a cathedral for safe keeping. When released Azerrad will attempt to turn the summoner into a vampire, under its control.
23. Dalanboge, the Feaster Upon the Dead
Dalanboge is a demon of pestilence, corruption, pollution, and death. It is also known as The Mirror of the Abyss, and the Goldmonger of the Underworld. This particular demon appears as a murdered version of the summoner, and will attempt to slip away unnoticed. It will begin killing, and each person it kills becomes another lesser demon of Dalanboge that can be manifested. These infernal zombies do not lose skills or abilities, but gain a chaotic evil alignment, fanatical loyalty to Dalanboge, and have a unified vision of raising an infernal army to wage war against the living. Dalanboge is a prankster and a trickster at heart and likes toying with victims and being as perverse and gross as possible. It's Pazuzu meets Jackass.
24. The Devourer of Dreams
The Devourer of Dreams is a non-corporeal entity that only appears in dreams of those it has touched. It will continually assault victims through their dreams until they are killed in said dreams. After this, they become the dream-eaten and mortal servants of the Devourer. The Devourer was only stopped when it was trapped in a magic lamp both inside and outside of the dreamlands. If the summoner masters the Devourer of Dreams they can gain the powers of a Dreamwalker and travel to and from the Dreamlands with ease. If they fail, they become the first victim of the Devourer of Dreams
25. The Silent Stalker
The Silent Stalker is a gug who was trapped in a magic lamp, ending its reign of terror decades ago. Releasing the gug allows it to go back to its hunting grounds and resume its killing. If the summoner masters the Gug, it will become their silent shadow and will grudgingly do as it is commanded, unless it is commanded to kill, that it will do with great enthusiasm. The Stalker has a strong sense of self-loathing, and hates mirrors. To this end it will find a mask to cover its face. Lacking one, it will make one from the skin of its victims.
26. The Immaculate Artisan of Pleasure and Pain
The Immaculate Artisan of Pleasure and Pain is an immortal flayed one. Having tremendous magical power and dominion over other flayed ones and imps made it a powerful adversary, but the Artisan was vain and egotistical and was defeated in a contest of riddles, and was accordingly trapped in the lamp. Once released, it will serve the summoner in a monkey's paw fashion and wont challenge for control until the summoner is a suitably weakened or compromised position. The Artisan has magical power on par with an archmage but is specialized to illusions, evocation, and creating charms and wardings over others. It is also able to raise the dead back to life, and reduce a person to a red mist while keeping them alive and fully aware of their pain.
27. A Pessimal Beast
The Pessimal Beast is a cursed abomination, a beast that gains the memories and emotions of those it consumes. Sentient, intelligent, insane. Those who trapped it, finally, could not bring themselves to slaughter it, as it still had their slain comrades voices and memories. Instead it was imprisoned in a lamp and left to be forgotten while the victorious grieved. Once found and released, the massive plant like animal will seek a moist environment to hide in and being hunting to feed itself. If mastered in a contest of wills, it will serve the summoner, and will answer any questions it is asked. Feeding it fresh victims is a cruel way to interrogate them.
The entity known as Mahoganaea is a gaian worm of impressive size. When unleashed, Mahoganaea will appear and mindlessly begin moving away from the summoner towards the most obvious disruption in the environment, leading the gaian worm to plow through and devour townships, cemeteries, fortifications, and areas of blight and corruption. In ages past, a powerful kingdom bound a number of gaian worms into lamps and would use them to restore desolate or contaminated areas. Eventually they started using them as unintentional siege engines, instead of agricultural implements, something most scholars believe to be the tipping point of the kingdom.