Fog

Fog on land is usually an inconvenience, but at sea it can prove disastrous. Decreased visibility makes navigation more difficult, and the crew might not see a hazard ahead until it is too late to avoid.

Each time you enter fog, there is a 1-in-6 chance that it is an Eldritch Fog. Checks made to navigate through an Eldritch Fog are made with disadvantage.

For each Watch you spend in fog, the Crew and up to 4 Officers may each contribute to a Group Check to navigate safely through. Eldritch fog lasts at least 1 Watch, while regular fog lasts at least 1d6 Watches - any Group Check success starting on the last mandatory Watch causes the ship to leave the fog.

d20	Severity	Fog Visibility*	Eldritch Fog Visibility*
1-9	DC 10 - light	Less than a mile	60 feet
10-15	DC 15 - moderate	Less than a quarter mile	30 feet
16-19	DC 20 - heavy	Less than a hundred yards	15 feet
20	DC 25 - oppressive	Less than sixty feet	5 feet

*Note: Everything within the fog is at least lightly obscured. Everything beyond the "visibility" range is heavily obscured, and therefore can't be seen at all.

Result	Effect
3+ successes, 0 failures	Total Success - the fog has no effect on navigation, the crew's quality increases by 1 for a number of days equal to 1d3 + 1 for each success above 3
More successes than failures	Success - the fog slows the ship, reducing its travel pace and speed by half
More failures than successes	Failure - the fog slows the ship and disorients the crew, reducing its travel pace and speed by half and causing it to move in a random direction
No successes	Total Failure - disaster! the ship moves at half speed in a random direction for 1d4 hours, then runs aground

d4	The ship has run aground on...
1	island - beach
2	island - rocks
3	reef
4	sand bar

Types of Eldritch Fog

1. Ghost Fog - The mists contain the souls of murder victims whose bodies were thrown into the sea. A cold shiver runs through your body when you enter the fog, and religious folk sense something deeply unholy here. The souls of the dead want the living to join them - every hour, there is a 50% chance that hostile incorporeal undead appear and attack those on the ship (2d4 specters, 1d4+1 ghosts, or 1d3 wraiths). If a humanoid creature dies in ghost fog, its spirit rises as a specter that is hostile toward all creatures that aren't undead. All non-undead in ghost fog are vulnerable to necrotic damage.
2. Shadowfell Fog - An oily fog seeps into the material plane at thin points in the boundary between the two planes. The slimy mist seems to sap your strength and motivation, and cause despair among the crew. Each hour, the crew must make a quality score check with a DC of 8 + the number of hours the ship has been immersed in shadowfell fog. On a failure, their quality score decreases by 1 while within the fog, and for 1 day thereafter - both the penalty and duration are cumulative.
3. Wild Magic Fog - As you enter the mists, you feel your hair stand on end, and catch the slight whiff of ozone. Few know the origins of wild magic fog - some claim it was created by capricious gods, while others insist it is the result of magical experimentation gone wrong. Whenever a creature in wild magic fog casts a spell of 1st level or higher, roll on the Wild Magic Surge Table.