My characters are in the middle of a magic-industed rainstorm that has lasted days. They're about ready to fight in an area that is covered in thick mud. I'd like to figure out some rules that make combat a bit harder. Between the ankle-deep mud and torrential rains.
Any advice?
Deep mud is difficult terrain. No running, charging, or 5' steps.
Rules for rainstorms are in the Core Rule ook under environment.
^^^
Additionally, you could add other effects to the mud to make it harder to fight in. For example, adding a Reflex save or a STR check each round to avoid being stuck in the mud, making those that fail unable to take any move actions, become flat-footed or both.