The pyromaniac ailment can be acquired during random event during crossing hex with fire. Character with this ailment has a relatively high chance (50%) to set up fire on hex adjacent to just explored structure, or on hex adjacent to position where the Trek is standing. This ailment is active even with Sanity above 0.
Setting a fire is possible after:
Setting a fire is not possible after
- visiting a native village.
Having a pyromaniac in your team is sometimes useful due to terraforming jungle into scorched earth which reduces sanity travel cost from 8 to 3. What is more, "fire kills roaming animals on adventure map"(?).