A plot booster is a concept used in Legacy-style board games, being an unknown element added to a certain game and thereby changing certain rules that players are used to.
In Magic[ | ]
In connection to Magic: The Gathering, a plot booster named "Uncovered Cavern" was first mentioned on the test card Planequake in the Mystery Booster set. No such booster pack is part of that set in reality, much like Contraptions weren't part of Future Sight though they were mentioned on Steamflogger Boss.
It may be assumed that if the plot booster would be opened, its mysterious contents could be added to a game of Magic while it is in progress, changing the playing environment drastically. A plot booster can only be opened if certain circumstances are met.
Example[ | ]
Example
Planequake 
Sorcery
Planequake deals X damage to each creature without flying and to each planeswalker. If X is 10 or more, open the “Uncovered Cavern” plot booster.
Rulings[ | ]
- If you don't have the appropriate unopened plot booster when instructed to open one, that part of the spell or ability's effect is ignored.[1]
- Creatures and planeswalkers dealt lethal damage by Planequake won't be destroyed until state-based actions are performed, after you've opened the "Uncovered Cavern" plot booster if applicable.
See also[ | ]
References[ | ]
- ↑ Eli Shiffrin (November 11, 2019). "Mystery Booster Release Notes". magicthegathering.com. Wizards of the Coast.