Adapted from one of the Arduin books (I forget which one).
This large golden platter is usually held by a statue in some deep, dark, and super-dangerous dungeon. At the foot of the statue is a plaque which reads in a long-forgotten tongue, something about eating if you believe the gods are on your side, etc. Read languages will easily decode the message, or possibly an intelligence check for a bard or some PC with a background in linguistics.
On the platter are three items - a loaf of wonderful-smelling bread, a large piece of juicy roasted meat, and an ornate chalice filled with a rich, dark wine.
Should the PCs be brave enough to partake of this feast, here is what happens.
Guidelines: There is only enough of each item to benefit (or screw over) one person. A single person may only benefit from one of the items.
For each item consumed, roll a d10. All effects are permanent.
1-3: Strength/Agility/Stamina (STR/DEX/CON) are reduced by 1d4.
4-10: Strength/Agility/Stamina (STR/DEX/CON) are increased by 1d4.
1-3: Personality/Intelligence/Luck (INT/WIS/CHA) are reduced by 1d4.
4-10: Personality/Intelligence/Luck (INT/WIS/CHA) are increased by 1d4.
1-3: PC loses 1d4 levels.
4-10: PC gains 1d4 levels.
Theoretically, one person will get screwed over, but of course it all depends on the dice gods. PCs should have at least a hint of what they are getting themselves into - perhaps rumors could be dropped in well beforehand. Just be sure you are okay with following through with it if a PC with bad luck loses 4 levels!
In our game, the level 5 cleric lost 3 points of Per/Int/Luck. The level 6 barbarian gained 4 points of Str/Agi/Sta. And the level 6 ranger leapfrogged to level 10!