The big focus in the exploration section will be on surprise and evasion. Avoiding surprise is an Avoid Accident roll for both sides. Lots of things can negate surprise for one side: anyone carrying a light source can't surprise an opponent in a tunnel, although they can still surprise an opponent behind a door. Breaking down a door negates surprise unless it's successful on the first try. Successfully listening through a door negates surprise, as does ESP or any other successful means of detecting monsters (smelling a particularly odorous monster behind a door, for example.) A surprised adventurer or creature must make an Avoid Accident roll to avoid dropping held items (this is slightly more likely than the LBB's 25% chance, but keeps things easy for GM rulings.)
Wandering monsters will in general be 2d4 x 10 feet away when first noticed. Change this to double light radius, if the monster is carrying a light source in a long, straight tunnel (in mythic underworlds, this should never be the case, since all monsters there have permanent infravision and thus no need of a light source.) Divide the distance by three if the party is surprised. Modify the distance based on physical obstacles.
In the underworld, evasion is impossible if the party is surprised, the monster isn't, and the distance is 20 feet or less. This situation may change later through the use of magic or tricks. Otherwise, pursuit is automatic as long as the chase is in a straight line and the monster doesn't fall more than 90 feet behind. Obstacles and diversions have a chance of ending pursuit: use an Avoid Accident roll for the monster, +1 difficulty if the party enters a secret door. Dropped food or treasure can distract a pursuer: make a roll for the party, based on monster's intelligence, to see if the ruse works:
- intelligent: Avoid Danger for treasure; Change Situation, +1 difficulty for food
- semi-intelligent: Avoid Accident, -1 difficulty for either
- non-intelligent: Avoid Danger for food; Change Situation, +1 difficulty for treasure