Note: I got 5 out of 6 ingredients very nicely, in my opinion. I tried and tried and tried on the last ingredient, but ultimately just tacked it on. See if you can guess which one

.
Ingredients
Amnesia
Island Fortress
Evil Monks
Eggs
Hangman Tree
Cursed Spear, Back-biter
Eggs of Doom
Summary: The PCs stumble across a Fabergé-like egg that intends to destroy them all. Unfortunately, it's practically indestructible, so they have to bring it to the site of its creation, where the means to break its vicious cycle lay. It's nastier than it sounds.
Foul Enchantments
Once upon a time, there lived a foul and wicked enchanter. He was a bitter man whose once good intentions had always gone astray, and instead of blaming himself, he blamed all else - gods, men, the cast of the sun, anything but himself. Eventually, consumed by his own desire for vengeance against all of his own failures, he crafted a plan to punish as many as he could feasibly arrange, long after his own inescapable death.
Although his name is long since lost, his final revenge lives on. Twelve finely crafted eggs of gold, silver, platinum and numerous jewels, given as gifts to various leaders of religious and secular bent both, are scattered about the world. Each has a particular power, and a malevolent intelligence guiding it. The less subtle ones have long since been destroyed, but there still exist an egg of charming, an egg of forgetfulness, and an egg of betrayal, all subtle enough to survive and continue their creators will.
All of the eggs are essentially indestructible - those that have been destroyed in the past, were destroyed at the enchanter's original tower, which is now guarded by one of the eggs to prevent the same happening in the future.
Egg of Charming
This golden egg, studded with rubies and an engraved mural of a festive party, was given to the head of a monastic order, and has remained with them since, slowly shaping the monks into a bastion of order and discipline.. one that dominates the surrounding lands by the iron fist of fear. The egg of charming can utilize a wide variety of charms such as
charm person and
dominate, but it prefers careful use of
suggestion and controlling key people to influence others.
Under the influence of the egg, the monastery has relocated to the enchanters original home, a small tower fortress on a small island at the center of a modestly sized lake. Here, the egg (by way of the monks) guards the vault that the enchanter crafted to control the eggs... or destroy them if they turned on him.
The rubies gleam a little too brightly when it is using its powers.
Egg of Forgetfulness
This silver and brass egg is a marvel of clockwork which perpetually cycles inside the framework shell. It has wandered from hand to hand as it tires of (or destroys) its present owner. Not quite as subtle as its two remaining brothers, it has still managed to conceal its curse well enough.
The egg has three essential powers:
1) Attraction: Target must be within 5 feet. Target must make a Will save; on failure, target attempts to touch the egg. Once you touch the egg, it can affect you with its other powers. On success, nothing happens... and the target is unaware that anything almost happened. However, a success also means that the egg can not attempt it again for 24 hours.
2) Total Amnesia: Contact required, the subject puts the egg somewhere safe, or gives it away to a stranger, and completely forgets the egg's existence. The egg usually waits for its subject to be alone before attempting this.
3) Spells, as a 10th level sorcerer (including spells per day, with CHR 14): Daze (0), Sleep (1), Erase (1), Obscure Object (2), Detect Thoughts (2), Misdirection (2), Undetectable Alignment (2), Nondetection (3), Secret Page (3), Confusion (3), Rary's Mnemonic Enhancer (4), Feeblemind (4), Modify Memory (4), Mind Fog (5). All of these spells have a range of
touch and area of
one subject instead of their usual stats. The egg usually uses Rary's Mnemonic Enhancer to persuade its owner that it is beneficial to the owner's memory.
Essentially, the egg uses all of these spells to conceal its true nature, cause its owner to forget things at inappropriate times, rewrite the owner's calendar book (reverting to normal later), and so on... turning even the most devoutly disciplined of owners into a flaky wreck. It prefers owners with a lot to lose, naturally.
Egg of Betrayal
This platinum egg is constructed of a clever series of sharp-edged rings with bits of emerald between them. The wave-shaped edges and faint green reflections from the emeralds makes it look sea-like. Small cuts, similar to that received from crisp paper, are common among its owners. This is its natural appearance, but not the only one it might have...
The egg is somewhat animate in its own right, and can
shapeshift into useful items. In most such situations, it can be treated as a +3 item or weapon, and that's exactly how it behaves, until it finds a good point at which it can betray its owner. At that point the item will fail the owner, usually catastrophically, before shapeshifting into a good form to escape in. Divination magics will also reveal it simply as a useful magic item. However, once it betrays someone, it must flee and hide, as it will shift back to its natural state a few rounds later, and can not shift again for an hour.
It is currently in the form of a spear.
Hangman Tree
This is the monk's symbol: it is tacked on to their crest.
The fortress also has one in the central garden, where it may inconvenience the adventurers.
Hook and Sinker
Hooks
Monte Maul: Both the egg of betrayal and the egg of forgetfulness masquerade as far more useful items. Have the PCs find one or the other amongst other, lesser treasures. They should be the best items in the bunch.
The egg of forgetfulness should be introduced long before you intend to run this. The Rary's Mnemonic Enhancer is very useful, and any mage should be quite happy with the egg's ability to provide it to him. Over time, however, begin introducing hints. Don't tell the mage about a party, but have an NPC ask him why he wasn't there... and insist that he was invited twice. Have an attractive NPC he's never met greet him as a dear friend (or relative!) and be insulted when he doesn't know them. Have one of the mage's other items turn up missing (he set it down on a table somewhere and forgot it). Don't forget Will saves for each event, of course - on a successful save, just hold off for a day.
The egg of betrayal can be introduced anytime. As a spear +3, it should be attractive to
someone. More so than the egg of forgetfulness, this one has the potential to be an actual villain - when it finally attacks (in the middle of a very, very dangerous battle, it sneak attacks a friend or its owner), it will attempt to shift forms and flee.
In either case, the items can not be normally gotten rid of. The egg of betrayal will show up as a different item in a different horde. The egg of forgetfulness is even more insidious, as the PC will simply plan to get rid of it, and forget to do so.
Alternate Monte: This is a twist on the above. The items have not yet been found out. Have the PCs hear a rumor about a
third egg in the same series... one guarded by evil monks and kept in a tiny fortress, where they use its wonderful powers to spread their villainy.
Someone Else's Problem: Someone else has one or both of the eggs, and hires the adventurers to help them. Or rather, their beautiful daughter does ("Dad always had a perfect memory, and I think that egg he got is doing this to him").
Sinkers
The plot is fairly straightforward. Get the eggs to the fortress, beat up the monks, put the eggs in the destruction device, and get rid of them. Maybe round up any other eggs they hear about while they're at it. The difficulties lie in the subtle evil of the eggs, and the PCs will have to be clever (and work together closely) to defeat the memory problems, and to keep a hold of the egg of betrayal (which, once their path becomes clear, will probably be trying to escape constantly).
How difficult is up to the DM, of course, based on the abilities of his players. But numerous precautions will definitely be needed.
The egg of charming may or may not be encountered - it prefers to work through others, and would likely avoid directly confronting/charming the PCs, as it can't handle them all at once.
You can twist this scenario up a bit, and have one or more of the eggs plotting to destroy the others while saving themselves. The egg of forgetfulness could
modify memories to make the egg of betrayal look bad. The egg of betrayal could avoid betraying its owner, and actively help the owner fight the monks, only to escape after the other eggs go in. The egg of charm could send the monks on a holy quest to destroy the other eggs... perhaps even hiring the PCs to help them contain them.
You could also stretch it out a bit. The egg of forgetfulness makes a good intelligent foe that most people would be inclined to underestimate. The egg of charming and its monks could also be a good long term villain.