Thanks for all the help everyone! Here are the more "formal" results of this thread. I thought I'd post them in case anyone else wanted to use them.
Fog reduces overall depth of vision by ¼. All characters in the company must make an Agility roll or suffer a level of Fatigue from some minor injury. It also doubles the company’s chance of getting lost. Draw an extra encounter card. If the card is 5 or above, an encounter occurs. If a face card is drawn, the company is automatically surprised and their opponents have The Drop on them for the first action.
It rains daily in the Zin Marshes. What starts as a simple rainshower for the company becomes a battle for life and death as they find themselves caught up in a torrent of raging flood waters.
Swimming rolls -2 are required of all characters. Use the Drowning rules to determine injuries and chance of death. Deal initiative as normal. Those characters dealt a face card have a chance to grab hold of something substantial and with a successful Strength roll may drag themselves to safety (remember encumbrance modifiers!). Those who are dealt a Spade are caught by an undertow and suffer an additional -2 to their next Swimming roll.
If a Joker is dealt, it is treated like a face card, and the character is awarded the standard +2 bonus to all actions that round. Unfortunately, it also indicates an encounter of some sort!
The characters have wandered into an area where thick patches of compost and decay can release dangerous pockets of gas. Any exposed flame has a 2 in 6 (1-2 on a d6) of exploding, causing 2d6 fire damage to all within a small burst template centered on the flame.
A seemingly endless swarm of tiny, biting, blood sucking insects has discovered the company and found them to be an acceptable food source. The swarm will pursue the heroes one hex beyond the one they were encountered in.
All the characters must make a Vigor roll -2 or suffer a level of Fatigue. A critical failure indicates a character has contracted a disease, or that an insect has laid eggs in the character.
Disease: Beginning the next day, the victim is fatigued and feverish. He suffers a level of fatigue and must make a Vigor roll or have his movement reduced by half. On a critical failure, the sickness escalates and the fever becomes incapacitating. Draw a card from the Adventure deck:
• If it is a face card, the victim hallucinates that his companions are a threat to him! He will recover enough strength to fight off this perceived threat and attempt to escape into the forest, eluding capture as long as possible. The character can maintain this level of strength to move 1 hex before collapsing unconscious and comatose (and easy prey for any passing creature).
• If it is a Joker, the victim makes a miraculous recovery, but has become highly contagious. All members of the company must make a Vigor roll +1 or contract the disease!
Healing rolls can keep the disease at bay, but will not restore Fatigue until the victim can rest for 24 in a clean, cool place.
Larva: Beginning the next day, the larva will hatch and begin feeding beneath the skin of the victim. The victim suffers a level of Fatigue and must make a Vigor roll or have his movement reduced by half. On a critical failure, the itching and pain is incapacitating. Draw a card from the Adventure deck:
• If it is a face card, the victim grows mad with hunger. He will gorge himself on everything available to him for the next 1-2 days, even to the point of eating raw meat if it is available. After this period, the victim falls comatose for 24 hours, at which point the larva emerge from his body, doing 4d6 damage (armor does not protect from this) and becomes a new insect swarm to plague the party (and potentially repeat the cycle).
• If it is a Joker, the victim makes a miraculous recovery, or at least appears to. Instead, the larva form a sort of hive mind that exert a level of control over the character. They will attempt to lead the company to the nest of their queen – a monstrous, bloated insectoid beast that is a terror in battle!
The company has stumbled upon a trap laid by some other denizen of the marshes. Deal cards from the Adventure deck. The character(s) with the lowest card value has stumbled into the trap. If the trap is detected (Notice roll -2), it can be avoided. Whoever set the trap will surely return to tend to it in 1d8 hours, and will likely bring company with him.
• Spiked Pit: 5 yards deep; 2d6+5 damage. 1 in 6 chance another creature has been trapped here already (GM choice). This is the classic tiger pit.
• Snare: The character is caught by the leg(s) and hoisted 5 yards into the air, suspended by a rope.
• Vice: The classic bear trap! The character’s foot is caught in the vice, causing 2d8 damage and reducing his Pace by 1 until properly healed.
PRESERVATION OF GEAR AND RATIONS
Due to the overwhelming humidity and the difficult terrain, the company must take special precautions to preserve their gear in the journey through the Zin Marshes. Each day, the character must make a Survival roll to properly prepare their gear. Failure indicates that a random piece of gear will fall victim to rot or rust.
d10 Affected Gear
1-3 Rations: 1 day’s worth has become fouled.
4-5 Water: 1 day’s worth has become fouled.
6 Rope: 10-40 (1d4) feet have become rotten.
7-8 Clothing: The character is afflicted with some manner of fungal rot and suffers a level of Fatugue until the body part is allowed to dry and be properly treated.
9-10 Weapon: a random weapon in the character’s possession is rusted and does –1d damage until repaired. Furthermore, on a Fighting roll of 1, regardless of the wild die, the weapon breaks or rendered irrepairable.