Our campaign had several important entities which moved of their own accord.
It was important not to force these encounters on the players in a specific session. Given the West Marches format, a referee might not know on what in-game day their session would start. So to help us coordinate, we created systems and used them to generate months of movement in advance.
The first was the juggernaut Llamon, on Ruislip at Donenashoe (03.09). Llamon was blinded by the players and went on a rampage. We figured it would charge around Ruislip and eventually settle down.
To simulate this, we rolled 1d6 to determine the number of named locations it would destroy. We then rolled 1d6 to determine a random direction, rerolling this if it reached a location or hit a coastline. Naturally, its first destination was Dorbog (01.10), which is somehow marked for destruction in every Wolves campaign.
Another group of players woke Sruthkin (02.16). They escaped with their lives by promising the dragon more treasure. This is a bad idea - a dragon is impatient and capricious, and may arrive at any moment to collect. We decided the best way to handle Sruthkin was to put him on every encounter table, until either he or the players were destroyed. In the end, he was petrified with the head of a medusa.
When the players landed in the Ergyng region of Albann, we began keeping track of The Roaming Court. At first we used a random walk, rolling 1d6 to determine a random direction each day. This was too erratic and resulted in a lot of revisited locations. Eventually, we put together a hex to steer the court based on the previous days direction of travel. This is similar to the rules for wind direction. The following allocation resulted in sweeping curves with the occasional sharp turn.
The Roaming Court’s movement hex.
We took the same approach for Mab’s Mob - a People’s Crusade charged by Archibishop Mab in Cernyff (08.14) to invade Moerheb Weald and destroy the Fallen Druidic Circle (14.18). We figured a mob of peasants would be erratic in the dark forest, but we eventually wanted it to reach the druid circle. This allocation of results gave it a zigzagging path. The mob passed encountered the werewolves of Rhedynfre (12.17) and the dryads (13.19) before veering to the druid circle after 9 days.
Mab’s Mob’s movement hex.