Encounter Design 101: Traps!
In the movies, traps are big dramatic sequences that bring the hero within a hare’s breath of certain death, only to be escaped at the last minute by a quick wit or sheer luck. In RPGs, traps are most often an obstacle that cost the heroes resources they would rather spend elsewhere (bennies, wounds, fatigue, or sometimes equipment!).
When you include a trap in the encounter, you need to consider a couple of things. Is it the focus of the encounter, or is it an additional obstacle? How easy is it to circumvent or disarm? How dangerous is it?
If the trap is the focus of the encounter, it should be dangerous, complex, and bedeviling. It can have multiple parts. Consider the trapped corridor from the beginning of Raiders of the Lost Ark. Rolling bolder, poison darts, spiked pit, and spear trap all work together to create a very tense scene. These traps are sometimes what are called “deathtraps” and involve sharks with laser beams or at the very least, irritable mutant sea bass. They are usually there to protect something very important (Raiders) or are designed to kill those who displease the villanous creator (James Bond).
If the trap is an obstacle, it is something that must be avoided as part of a larger encounter. Fighting a monster that can jump doesn’t seem like a big deal, until you add a bunch of pits and give the monster the ability to push a character into one. Or maybe its some magical beam that every round zaps someone in the room? Sure it might zap your monster, but maybe the monster is tough enough to resist the damage, or there are just so many monsters you can afford to lose a few. Either way, the trap needs to be a threat.
The best traps are either those the players don’t see coming, or those that work together to be a real thorn in their side. They shouldn’t kill outright, but they should require some work or sacrifice on the part of the players to avoid.
You can find a list of basic traps in the Warlords of Aros Bestiary.