Tomb of Annihilation: Hex crawl procedure

As previously noted, the first half of Tomb of Annihilation largely consists of a hex crawl. This means that, outside of keyed hexes with static encounters, the game in this portion consists of procedurally-generated content. Do the adventurers get lost? Do they have enough supplies? Do they have any random encounters?

For my own needs, I assembled the following notes from the adventure book, the Player’s Handbook, and the Dungeon Master’s Guide. In a few places, the written guidance has some missing parts, so I filled in and noted accordingly. If you handle those parts differently, I’d love to see what you do!

UPDATE: My friend Juan pointed out where DMG page 111 provides more food and water on successful foraging than I realized.

UPDATE 2: Added more notes on Ranger and Wanderer. Merged water and food check step.

Daily Procedure

1. DM determines location on map.
2. DM determines weather. Roll d20:^(*)
   • 1-16: Occasional light rain: proceed as normal
   • 17-19: Heavy rain: Visibility limited to 150 feet
   • 20: Tropical storm: travel by canoe impossible, travel on foot gains 1 level of exhaustion, DC 10 Constitution save for another. Disadvantage on checks to avoid becoming lost
3. Party determines navigator, pace, direction:
   • Normal pace: 2 hexes per day by canoe, 1 hex per day by foot. For rivers, upstream and downstream have no effect, and waterfalls occur every 10 to 20 miles (requiring portage of canoes).
   • Slow pace: 50% chance of 1 fewer hex per day, can hide from encounters or approach stealthily
   • Fast pace: 50% chance of 1 more hex per day, -5 to passive Perception
   • Parties with a Ranger are not slowed if in their favored terrain. Therefore^(*), they gain the benefits of a slow pace without the chance of 1 fewer hex per day.
4. DM rolls Wisdom (Survival) for Navigator:
   • DC 10 for coasts and lakes
   • DC 15 for jungles, mountains, rivers, swamps, and wastelands
   • Add to roll +5 for slow pace, -5 for fast pace
   • If lost, roll a d6 to determine which neighboring hex the party enters. Players are not shown their location on the map in this case.
   • Parties with a Ranger in their favored terrain cannot become lost in normal navigation.
5. DM rolls d20 three times for random encounters (morning, afternoon, night). On a roll of 16 or higher, roll d100 and consult Appendix B based on terrain and, if in jungle, level of undead presence. Insert as appropriate during the travel sequence.
6. Party checks for dehydration and malnourishment.
   • Characters can forage water if they succeed on a DC 10 Wisdom (Survival) check. A similar check can yield foraged food.
   • A successful forage yields (1d6 + Wisdom modifier) gallons of water or pounds of food, although each type of forage requires its own roll.
   • Foraging characters do not contribute to the group’s ability to notice threats.
   • Rangers in their favored terrain gather twice as much food and are able to notice threats while foraging.
   • Water from rivers and lakes should be boiled first.
   • Raincatchers (ToA p. 32) can catch 2 gallons of water per inch of rain and hold up to 8 gallons.
   • On heavy rain days, roll d4 for inches of rain. On storm days, assume full 4 inches or more.^(*)
   • Characters with <2 gallons of water must make DC 15 Constitution saving throw or gain 1 level of exhaustion (disadvantage if wearing heavy clothing or medium or heavy armor). Traveling at a fast pace adds -5 penalty to this saving throw. (According to the PHB, if the character already has one or more levels of exhaustion, the character takes two levels.)
   • Characters with the Wanderer background feature (typically Outlanders) can automatically find food and fresh water for themselves and up to five other people each day in suitable terrain.
   • Expend 1 unit of rations (1 pound of food).
   • Each day after (3 plus Constitution modifier) days without food, a character gains 1 level of exhaustion. A normal day of eating resets this counter to 0.

(*): These steps are not found in the published game materials and may be altered at DM’s discretion.

Exhaustion effects

Level	Effect
1	Disadvantage on ability checks
2	Speed halved
3	Disadvantage on attack rolls and saving throws
4	Hit point maximum halved
5	Speed reduced to 0
6	Death