Every key (literal or metaphoric) has one or more keywords describing it: brass key, iron dragon key, crystal goblin key. Doors, chests, and other locked items also have key words.
When attempting to use a key to unlock a lock, roll 1d6 for every keyword that matches. Example: the red crystal key used to unlock the blue crystal door only has one matching keyword, “crystal”, so roll 1d6.
If any of the dice results is 5+, the key fits the lock and opens it. Otherwise, it doesn’t. If the key doesn’t fit and snake eyes (double 1s) are rolled, the key breaks in the lock.
Tougher doors, particularly those on lower dungeon levels, have more than one lock and thus need more than one key.
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