How to handle that?
With a sufficiently large rumor table, you could just have the player roll their Wisdom or Intelligence bonus number of times on the target specific rumor table, and thereby learn something about the monster/location/ruin/villain. This preserves the mystery about the target item, but still provides some (possibly true) information about the target. (could also work with Charisma, if it is knowledge gained from being around town)
Rangers get +1 roll on the table for monsters, wizards +1 for magical items, clerics +1 for gods, and so on. Bards (if they exist in your game) get to know if one rumor is true or false (being that they collect knowledge).
Could also be used for generic rumors for town without having to have the players say "are there any rumors?" or some such cliche.
Here is an example, using some information from Hack & Slash about the Cockatrice.
Rolf, the 3rd level Cleric of St. Cuthburt has a +2 Wisdom bonus. When presented with the question "what is a cockatrice", he, like everyone of his culture, knows the following: it is a monster, like a bird, can turn you to stone. However, what else does he know? Since he has a +2 Wisdom bonus, he may roll twice on the d20 cockatrice rumor chart below.
- They can fly short distances
- Their gaze or touch can petrify people, even after death
- They lay eggs
- The weasel is immune to their petrifaction
- It doesn't actually petrify, but withers plants, scotches grass, and bursts stone from heat and its deadly breath
- The beak and claws of a cockatrice are made of iron
- The feathers are quite magical, and useful for arrows, quills, etc., but they must be used quickly
- A cockatrice grinds the stone it eats using hard diamonds stored in its stomach.
- Cockatrices are actually very wise and know many profound and secret thoughts of the origin of things, learned from the earth itself
- They are not natural creatures, they are created from a rooster of superior chickens and a still living snake plucked from the head of a medusa
- They are used to herd stone giant children and keep them safe
- They were designed by the wizard Vora Elgath, a wizard and friend of the stone giants who found them peaceful company
- The flesh of a cockatrice is quite delicious
- They love to line their nests with shiny sparkly items. The more shiny their nest, the higher the status among cockatrices
- They grow a crowstone inside their vestigial gizzards ranging in size from a grain of sand to marble size. This cloudy colorless gem is a potent cure for poisons and venom Swallowing the rank tasting stone is the most effective application. The larger the crowstone the more effective it will be
- Cockatrice feathers are useful as magical quills because of their durability against caustic substances
- The saliva of a cockatrice can turn stone back to flesh
- It is about the size of a goose
- They are impossible to kill by stabbing. Perhaps this is due to poison or perhaps their skin is resistance to piercing weapons
- The cockatrice is actually a passive grazing animal and not a predator at all. Their deadly gaze is for insects, not man