The Deck of Many Things
This was inspired by a conversation I had on instagram with nuolistarchild the other day.
'This is a ridiculous item and a complete campaign ruiner' were my initial thoughts, the Fates card alone can undo an event that has happened such as the Big Bad Evil Guy having never been conceived. Plot ruined. Giving a player the wish spell once can be dangerous, one card can give them 1d3 uses of wish.
Some cards can be dealt with quite easily but others can cause the campaign session to end because you'll have to rewrite your campaign in a Butterfly Effect style car crash.
If you are going to use it there are some tools you can use and have prepared just incase these you need them:
A 4th Level Knight NPC for your PCs to use as a minion
A spectral prison on another plane
A Devil with a vendetta
An Avatar of Death fight(s)
An NPC to turn against the party
An extra dimensional sphere where a PC can be imprisoned
Special items tailored to each PC
A Keep somewhere in the world for a player to own
The rest are pretty self explanatory and are dealt with easily, its all about losing their gear, wealth, intelligence or gaining riches or charisma proficiencies.
This item can be fun and can really shake up a campaign for a while. I would use this as a last resort if I'd run out of ideas or finished a long campaign and wanted a random start to the next story line. Also remember that the item itself can still work with 75% of the cards inside so you can nerf the risks involved. Using a prop is fun and can really energize your table too.
The element of chance really doesn't sit well with me, however, you could stack the deck in a specific way to explain an odd event in your game. If one of you players had come to you and said they have to sit out the next few sessions because of personal reasons but they still want to play; you could stack the deck in such a way that each player gets one draw each and get positive cards, your paused player draws the Donjon card. This makes the group about as powerful as they were before they lost a player and gives them a quest to find their missing companion. If you make the quest as long as the paused player leaves you've kept the game going while really not doing anything towards the main quest.
Here's one I prepared earlier...
