The Die of Fate
The Die of Fate from Burning Wheel is so valuable it travels between my games to be invoked when the players make a request that has no answer, this sole house rule has become pseudo-mystical among the Stalwart gaming group.

- Will they survive the fall off the cliff?
- Do they find something interesting while searching the old bookshelf?
- Is a well-known nonplayer character at the tavern this evening?
Your chances are between 1 and 6; on a 1, it happens. And it happens a lot; I have recordings proving it. The amount of times ONE appears is firmly in the realm of the supernatural, spooky—unreal even. The die knows what's on the line and delivers (or betrays) the best possible outcome.
This universal house rule has also expanded to the concept of a usage die or resource die from The Black Hack or, more recently, the Alien RPG by Free League.
Loosely described here, Resource Dice from the Alien RPG piggybacks on the Die of Fate and uses the concept of dice pools that diminish every time you tap an abstract resource. You could use this to track charges left on a magic item, arrows in your quiver, or time left in a spell. Create a pool of d6s between 1–6, roll, and deplete the pool by the number of 1s rolled until you run out.
I love this Dread-like tension. Rulings like these inform everyone the gamemaster is accountable for the ramifications they're setting, hitting that risk/reward bettor mindfeel as the dice pool diminishes or stays firm.
The physicality of it is a bonus, too, as abstract resources, such as food or water, can be traded or scavenged for, or just the feeling of running low on a necessary resource hits differently when it's a pile of dice versus a couple of variables on a sheet of paper. This opens up a whole facet of play left in the junk drawer next to encumbrance and spell components.
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