In game terms monster usually means an opponent that must be overcome by guile, negotiation, or force. Terrain can fill this role admirably, though negotiating with it may be difficult. Monsters also serve to regulate access to other areas, and often guard treasure, again, things terrain can handle. Terrain's biggest weakness, when considered as a monster, is that it doesn't really move, so initial placement is more important than with a typical monster. Similarly, pursuit situations are unlikely to result from a terrain encounter, though using monstrous terrain to affect the outcome of a pursuit is certainly an option. Here are a few guidelines when placing terrain as monsters:
Define the Threat - As GM you should have a clear understanding of what danger the terrain represents. A monster that represents no threat at all is not really a monster. Some of the typical threats posed by terrain include:
- Blockade - the terrain presents a real obstacle to travel. Part of the typical dungeon game is exploration and blocking terrain reduces opportunity for discovery unless overcome. Blocking terrain can also provide a tactical advantage for other monsters with a mode of travel unaffected by the terrain. Flying creatures often have an advantage when dealing with this sort of terrain.
- Division - the party is split by the actions of terrain, be it a swift flowing river, a deep chasm with a limited crossing, or maze-like passages presenting multiple confusing choices.
- Damage - falling damage is a favorite attack form for terrain-based monsters. Drowning (rivers and lakes) or burning (lava) are two other popular options.
Sketch the Solutions - I'm not proposing you come up with one true way to defeat the terrain, but think about reasonable approaches to resolving the encounter. You should reward your players for creative thinking in this regard so don't get too hidebound by whatever solutions you come up with. As part of this process it's also worth considering the long term ramifications of whatever solution the players use to defeat the terrain, they may well affect the local balance of power, particularly if the terrain presented a formidable obstacle.
Make it Worthwhile - Defeating the terrain monster should offer some reward to your players, otherwise they may see it as a grand waste of time. Treasure is one possibility, perhaps a less fortunate adventurer didn't quite make it across that chasm or pool. Access to a new area is another potential reward. Crossing that river of lava might open an entire area of the dungeon to exploration. Alternate routes are a third reward. Perhaps the underground river provides a means to bypass a particularly dangerous foe.
Terrain as the monster does have a few weaknesses.
- Static - Terrain generally doesn't move, so the decision to engage the encounter is totally up to the players. It's difficult as GM to 'play' the monster so leveraging a terrain encounter requires active interest by the players. Hints or clues that lead through monstrous terrain are a good way to encourage player interest.
- Magic - At higher levels of play, terrain can easily become trivial, especially if the party has access to magical flight or other transportation spells. Using monstrous terrain as a lair for a creature unaffected by the conditions is one potential solution to this problem.
- Eternal - Terrain usually lasts forever, so consider carefully before you place it. Defeating a terrain encounter once is interesting. Doing it every time the party goes by, less so.
Here are a few of the terrain encounters I used in my Moria game, along with the solutions implemented by the players:
The Spiral Descent - This is a large conical chamber with a single narrow ledge winding from top to bottom. One entrance is located near the narrow top, with two other exits near the bottom, which is littered with large, jagged boulders. The threat here is falling damage, and as the party discovered, a pack of annoying little Jermalaine occupying a network of tiny crevices and caves in the cavern walls. After demonstrating they could kill the Jermalaine if they could see them, the party began throwing food into the creature's den before beginning their descent, which negated the creature threat. This allowed them to easily defeat the falling threat using the relatively safe ledge (safe assuming they weren't trying to defeat Jermalaine traps along the way). The reward here (at least as far as the characters know), was access to the deeper caverns.
The Mud Pit - Several springs feed down sloping passages into this chamber, which is filled with thick viscous mud up to ten feet deep. The threat here is division and damage, with drowning in mud a real possibility for armored characters. Careful testing revealed a shallower path through the pit, and eventually one of the characters noticed someone had scratched directions in the ceiling of the cavern. With this information the room is fairly easy to navigate, and the party now has a hint that someone passes this way often enough to create the path through the room.
The Maelstrom - An underground river feeds a waterfall that splashes down into a lake-like chamber, then pours down a second passage into a broad swirling pool of water. A vast whirlpool sucks anything swept into the pool down and out of sight. The primary threat here is division and drowning (luckily no one fell into the pool). Unfortunately for the party, the stream bed provides the primary access route into the depths. The party overcame this obstacle by affixing a rope to one side of the swift running stream, allowing the them to traverse it with minimal risk. They got the idea (and a reward for defeating the Maelstrom) because someone had left behind a similar arrangement using a length of magical Elven Rope.
So there you have it, some thoughts on using terrain as the foe. Hopefully I've inspired you to give the rocks another chance. If this article was interesting, you may want to take a look at something I wrote last year entitled Approaching the Vertical, which also talks about elevation changes and terrain as features of the dungeon. Until next time, keep your ten foot poles handy and bring some extra spikes and rope!