Miasma is the fundamental danger in Crystal Chronicles. It poisons people, creates monsters, and isolates towns from one another.
In the original game, when a player left the safety of their crystal chalice (the container which is used to hold valuable myrrh, and which itself contains a tiny personal crystal) they would immediately begin to take damage, as their bodies were afflicted by the miasma.
For our purposes, let us say that the crystal chalice has an effective circle of protection 60 ft across. It is light, and easy to carry, but must be set down when the players are involved in combat.
When a player leaves this protective circle, they have a period of one minute to return to safety. If, after this minute, they are still in miasma, they must make a constitution saving throw (DC 15) or take 1 point of temporary ability damage to all physical attributes. After another minute has passed, if they are still in the miasma, they must make another saving throw, with the DC increased by 1, or take an additional point of damage to every score. This continues every minute until the player has either died, or returned to the safety of a crystal.