Something often overlooked by new players is that interating with a curio will quite frequently prompt you for an item to use with it, rather than simply operating the curio.
Failing to use an item when prompted will typically yield negative results, with some curios having much more dire consequences than others.
It's been reported that certain classes have different interactions with certain curios than other classes. Just because a curio in this guide may have a listed (or unknown) function, please don't be afraid to continue to experiment to see if you can discover anything new!
Also, a huge shout out to nepomucq and everyone over on this thread for getting the ball rolling with this. I'm just here to add the pretty pictures :P
Percentages are calculated based upon the value of the values reported in curioscurio_type_library.csv in your Darkest Dungeon folder. Values are up to date as of Build 10850
2016-01-19 - Release day! :D Curiously, it seems that only one new curio has been added to the game - The Ancestor's Knapsack. For those of you already making your way through the Darkest Dungeon, let me know what the story is (I'm just about to get started on a new save file so it'll be a while before I get there).
There was also a change to the Fish Idol, which has now changed its non-cleansing effects.
2015-09-30 - It's been a while! Build 10850 changes were incorporated. A couple of existing curio modifications, plus The Cove region curios were added.
Overall non-cleansing loot percentages changed
Disease is now no longer random. 100% chance of Black Plague
Makeshift Dining Table
Disease is now no longer random. 100% chance of Tapeworm
Curios for this region have now been added
2015-05-28 - Build 8855 changes were incorporated. Existing curio modifications:
Now found in all regions, not just Warrens
Can no longer be cleansed via torch
Holy water cleansing now removes a negative quirk instead of stress
Percentages to non-cleansing rewards have been modified
Can no longer be cleansed via firewood
In addition, a new curio was added:
Uses the same artwork as the curio previously known as 'Old One Statue'
Appears to be quest related. Cleansing looks as though it summons some kind of monster.
Curios can be found either inside rooms or corridor segments. Different locations contain different kinds of curios, but some varieties of curio are found throughout all types of dungeon. Each room may only contain one curio, while corridor segments can contain more than one curio. Differently from obstacles, curios do not prevent passage when not activated, and it is thus possible to leave them be to minimize risk, especially if there is a lack of correct provision items to trigger their benign effects. darkest dungeon curios items
Interacting with Curios
Once the party enters the room or segment that contains the curio, it can be clicked to activate a prompt. Through the prompt, the curio can be activated directly or with the use of a provision item: curios will react differently to certain items. Normally, the use of the correct provision item will trigger a positive effect, removing the chance of negative effects occurring, but there are exceptions.
Some curios grant loot upon activation. There is a fixed pool of items that can be looted by specific curios, but additional loot due to a low light level will be calculated separately and can thus be dropped even by curios with very specific loot drops.
Many curio effects such as stress infliction or heal, damage, the application of buffs and debuffs or the gain or removal of a Quirk affect individual heroes. The affected hero is always the one currently selected at the moment of activation. It is advisable, upon activating risky curios, to select a hero with good resistances or one that could potentially be affected by the negative effects without endangering the expedition.
Update: currently, as diseases have been reclassified as something different from a quirk, curios no longer cure diseases (i.e. Eerie Coral with Medicinal Herbs did not cure anything on a character with no quirks with the runs disease).
Sometimes, because of a Quirk the hero may have, they will interact with a curio without the player's consent. This is determined through Curio Types, with certain quirks respond to i.e. a hero with Bloodthirsty may interact with a Dinner Cart or Mummified Remains automatically when approaching it because of their shared "Body" typing. This can be dangerous since they will never use an item on their own when doing this, so there is a very real chance they will cause permanent damage to themselves. In addition a few of these quirks will also compel your heroes to steal the items that are looted, preventing the player from ever getting them.
While usually the only way a forced interaction will occur is because of a negative quirk, the disease Tapeworm and some afflictions can also cause a forced interaction.
Below is the list of quirks that force interactions, along with their type, chance of interaction and whether or not the quirk will inspire theft.