The Prison Lens

A mage of bygone days, Thyre Zerkail was both a scholar and a ruler of a city state, harsh but protective of his subjects, a summoner of no little power but no fool.
Often he used demonic minions to sew terror, dissent and chaos amongst his enemies, but he was well aware of 'what goes around comes around' and thus sought a way to neutralize his highly unreliable minions, and thus created a disc of meteoric iron and lead, cold iron and electrum.
When charged with power, the disc could entrap a severely wounded, dying or recently dead person in a non-space ... most useful for imrisoning demons, who tend to reurn and rise from being smitten over and over again!
Long years has it served him well, each demonic agent fionding himself first assaulted by a mage and his allies, then absorbd by a prison of dark metal, chained for all eternity. Thyre enchanted the disk so that it would stay in his general vicinity, so that nobody could meddle with it, and anytime a demon minion returned, it could be sent to the secure vault until kingdom come.
Then, the unlikely happened and the solitary magician began to care about one of his subjects in a very personal way, for the first time in his long, serious life he felt feelings blossom in his chest, all for but a maid, Shairne by name.
From a commoner he lifted her up to his apprentice and began to teach her, show her the wonders of the world, even travel, just to be with her. And blessed be the gods, she replied in kind.
All went well until again, an invading armyu threatened Thyre's city. Heptagram drawn and runes ready he called forth a minion from the abyss, and sent it to take the life of the enemy commander and his cadre. Before dawn, the beast was back, claws dripping blood. The mage set out to blast the beast to submission, and then to imprison it, but suspecting treachery, the fiend lurched forvard and severely wounded Shairne, the razor-like claws cutting deep. The disc, undiscriminating and unstoppable in its pull, claimed both the demon and the girl.
Great was Thyre's anger and sadness, but he was not one of those who would waste time - soon he had added an escape clause to his impregnable prison: true love could set one locked within free. And yes, soon the change bore fruit, and Shairne was returned to him, sorely wounded but alive.
His happines was restored, and Thyre was pleased.
Little knew he that the disk's magic was flawed when he hurried to bring back his love ... what he intended to do was that true love would set the one beloved free - anyway, who could truly love a demon, right? But the magic worked in a different way - sure, if you loved some specific prisoner, it would set him free. But the presence of ANY true love near the disk would release something for sure - in a very horrifying way, as the first time two true lovers had intercourse close to it, or a woman feeling true love, pregnant and in the presence of the object of her affection came near it, the child to come would be possessed with the spirit of a demon or other prisoner from within the disk, growing rapidly and most likely causing the death of the unfortunate woman, and releasing a hellspawn upon the world.
Soon, too soon their feelings for each other grew strong, and Thyre embraced Shairne in what was to be their first night of love ... great was then his surprise, as his beloved, exhausted from the act, suddenly swelled and burst open, one of his raging ex-minions standing amongst her remains. A second was enough, and Thyre too lay in a puddle of blood.
The disk, set to follow its master, was confused, and wandered off.

Magical Properties:

A disc, weighing about 150 pounds. It is constantly slightly warm, and very resilient - it must be able to be the focus of a gate! Sure, it can be molten by extreme heat, disintegrated or crushed by catastrophic violence, but no-one knows what could happen - it might even release all the prisoners, and no-one knows how many there are.

First is the intended purpose - the disc can be charged (half an hour at a node or nexus, eight hours by a single wizard, more can cooperate to cut the time) and is then ready to activate at the utterance of the command word (identify can reveal it) - it will then draw all sentients who are below 20% of their hit points, or recently dead, as well as demons traumatized from a very recent physical death, into a non-dimension, where all they can do is float and think, percioeving nothing, their physical functions suspended. The resistance roll against being drawn in should be fairly difficult, but automatic if you are not severely wounded or dead. The range could be something like 10 ft.

2, one who truly loves someone imprisoned (no hypocrisy!) can release a prisoner when rehearsing the loving feelings in the presence of the disc. The beloved will reappear in the state he was drawn in - wounded or dead.

3, then there is the risk of the undesired function - it WILL be triggered by true lovers within a very short range of the disc. The affected woman is simply unlucky, but will survive if strong healing magic is applied soon. Of couse, anyone nearby is exually unlucky, as they have to face a demon wearing a body this plane accepts as its own.

4, The most terryfying function is the disk's ability to inconspiciously teleport - it suddenly just sits there, but seems to have been there for some time, silently humming to itself. Sometimes, it will pick a person to follow around, always ominously just lying there, and impossible to get rid off - then someone else catches its fancy, and it is gone. The Prison Lens is not sentient, but it has a slight preferrence for following people capable of expressing strong feelings.

Imagine the random demon appearances - without a summoner, mysteriously killed lovers, and the creepy presence of a disk that just sits there...
Sure, the PCs could use it to entrap a rival, but who can make sure the disk will not simply vanish, and the villain appear, reborn? Keep in mind that the disc cannot cross teleport wards (it will try to stealthily float out, though, yet if restrained, it will be helpless.

It could be used as a hideout - you just hop inside, and have someone truly loving you then set you free when the danger passes. Just make sure you get some distance between yourself and the item before you express your gratitude! It can be used as a mean of rebirrth: mummy rot? lycanthropy? no problem - kill yourself and have someone activate the disc, and then wait to be reborn - with all your memories, of course, though if it takes too long, the void surely might drive you insane...

The possibilities are many, but you never know if you may allow yourself to truly love, knowing it is out there somewhere, and might telport under your bed when you least expect it...