Tinkering with Weighted WMTs

I first encountered the idea of weighted Wandering Monster Tables in the MMII, where encounter tables were designed to use 2 dice (1d8+1d12) to produce a number from 2-20. Due to the bell curve produced by this set-up, it is possible to arrange WMTs based on frequency — Very Rare, Rare, Uncommon and Common.

Recently, I have been meditating upon a different way to weigh a WMT based upon time. For years, my mom has had a bird feeder on her porch. In that time, she has noted that there is a general pattern as to when a type of bird is most likely to be feeding. It isn’t identical every day, but there are times when there are types of birds that will not be there.

One might use such a concept in a dungeon or wilderness area where the longer one stays, the more dangerous it gets because bigger and badder monsters come out to play. This could also be used in an area being contested by different factions. During the first part of a day, each side is preparing and planning, therefore most encounters at the beginning of a day will simply be one faction or another; however, later in the day (when these plans come to fruition), most encounters will find the factions in combat with each other.

To set up such a WMT, a chart with 19-23 slots can be made (the following example might be used in a 1st-level dungeon):

1. 1/2 HD Creature
2. 1/2 HD Creature
3. 1/2 HD Creature
4. 1 HD Creature
5. 1 HD Creature
6. 1 HD Creature
7. 1 HD Creature
8. 1+1 HD Creature
9. 1+1 HD Creature
10. 1+1 HD Creature
11. 1+1 HD Creature
12. 2 HD Creature
13. 2 HD Creature
14. 2 HD Creature
15. 2 HD Creature
16. 2+1 HD Creature
17. 2+1 HD Creature
18. 2+1 HD Creature
19. 3 HD Creature
20. 3 HD Creature
21. 4 HD Creature
22. 4 HD Creature
23. 5 HD Creature

To use the table, roll 1d12. For every hour spent in the area add an additional +1 to the roll. Thus, if a '10' is rolled for an encounter with an adventuring party that has been in the area for 4 hours, the final result will be 14 (10+4). If the party has just arrived and has yet to spend an entire hour in the area, nothing is added to the roll.

Using this method, such a table could represent an 8-12 hour period of time (where 19 slots = 8 hours and 23 = 12 hours). This would allow for the above process to be reversed with a 12 hour table (the 8 hour table would sit on the low end or high end of the table for several hours). Alternatively, one could add the bonus for every 2-3 hours and have the whole process cover a 24-hour period.