30 devious traps

30 Deadly Traps

1. The PC's Enter large round room, maybe 60' in diameter. Across the room is a stone door with a really tough lock. The Party's Rogue will have to pick it for a long time, or the fighters will have to beat it for a while before it crumbles.
   The ground is made of sand, and the ceiling appears to be made of glass, the topside of which is covered in gold coins. This is how you find out who the greedy guy in your party is. It only takes one projectile from a crossbow, sling, bow, etc. to completely shatter the glass. The weight of the coins causes it to break further, and all under the glass (everyone in the room) must make a Reflex save of whatever the DM deems fair or take 3d6 damage from the falling glass. About two rounds after, while everyone is buzzing around picking up gold pieces, they realize the glass was not only holding back coins. A poisonous gas begins seeping down towards the ground, and every round their in it, they have to make a Fort save or fall unconscious. That could put some pressure on the guy trying to get the door open. If they just run back the way they came, the DM could make it so that the room can't be entered again, and now they have to take "the long way" around.

2. The PC's enter a long hallway at a T-junction. There is a small step down into the hall, which appears to be about 70'-90' feet long and ten feet across. Down one end appears to be a dead in wall with a bunch of holes in it, down the other end appears to be a door. Once everyone is in the hallway, they here a grinding noise, and the floor starts to slowly move towards the dead end wall. They now notice the floor is made of rubber. The movement increases in speed until the PC's find themselves running. This is pretty much a big treadmill, and the wall with the holes in it now has spike sticking through them. Anyone who is taken into that wall will be impaled on the spikes for 5d6 damage (or however much you like.) In any case, the trick is to run as fast as you can, which could be difficult for heavily burdened or armed folk, and remember, you're only moving about 5-10
   forward a turn. About ten feet in front of the door is a stone platform that
   the players can jump onto for safety. For every round a PC remains on the treadmill, they have to roll a balance check of about 10 to stay on their feet. If they fail, then they lose about ten feet, and are that much more closer to the spikes.
   There is a switch in the wall on the platform by the door that many will mistake to be the 'off' switch. The trick is the machine starts when all feet hit the rubber, and stop when all of them are off. Whoever hits the switch only reverses the direction of the treadmill, knocking everyone still on it down and catapulting them onto the platform, perhaps breaking through the door.
   If you are the type of DM like I am, you will perhaps put some hulking bad guys on the other side of that door ready to hack & slash at the PC's who are out of breath and fatigued.

3. The PC’s get to the end of a hall, and come upon a chain dangling from a hole in the ceiling and a smooth stone slab door. Written on the door is the message “A test of Strength Lies Beyond”. If your PC’s are smart, they will make it so their heavy hitters and fighters will be the first in the room for what lies ahead. The chain obviously opens the door, simply pulling down on it with a Strength Check of about 12 will open the door quite easily. Whoever grasps the chain will feel as though the metal links are wet.
   When the chain is yanked, the door is raised and the fighters rush in, ready for battle, but find a nearly empty room. The room is 100' long, and about 50' wide, and completely dark. There is a small step down through the threshold, leaving everyone standing in shin deep water. About thirty feet away, hanging from the ceiling, about five feet above the water, are two, fat, parallel metal bars, arcs of lightning bounce back and forth between them.
   The PC’s will now hear a sickening, wooden crack. That was the ancient block and tackle system that allowed for such an easy Strength Check to lift a heavy stone door and two metal electrodes bursting into hundreds of pieces. The Strength Check to keep the door open and the electrodes in the air is now about 20 or higher. It should be noted that it is at about this point the PC holding the chain realizes his hands have been Sovereign Glued to the chain, and he cant let go. There are a few busted pillar pieces laying around inside the room the others could try to seek refuge on, but they would only allow one person to stay on. They could try to push these under the electrodes to keep them from breeching the water, but they weight about a ton a piece.
   Another PC may go back through the door and help the other keep the chain pulled so that the electrodes and the door don’t plunge, but they too, will become glued to the chain.
   If all else fails, and the PC holding the chain cannot keep the chain pulled down, all in the room are now trapped and will be electrocuted for 5d6 damage (or more >D) for every round the electrodes are in the water.
   The trick is that at the end of the room sits a small table, and on it sits a tube of Universal Solvent with enough for one application. If the person can make it back to the door in time, they can fix the PC right up, unless of course, there are now two holding on to it.
   Rather than just being a jerk, it might be a good idea to put a vast treasure in the room, give the PC’s reason to continue risking the chance of going back inside time after time.
   If another PC is glues to the chain, it might be an entire side quest in itself to find a way to get him unstuck.

4. The players come to a room with what looks like a chimney, which is in fact a tunnel leading up. It is about a 200 foot climb, but the chimney is studded with smooth stones for many foot and hand holds. The tunnel is narrow, so the players will have to go one at a time up the chimney. About halfway up, there is a trigger stone. Whoever trips the stone will afterwards be awarded a Concentration check of 20 to remember what the stone felt like. Rough, and sharp.
   The trigger stone releases a spiked weight that is in place at the very top of the chimney, and causes it to fall at an alarming speed. Faster than the PC’s can climb down, and they will probably find that just letting go and falling is the fastest way down. If the players make a successful jump check, the first ten feet of the fall go by with no damage, otherwise, every other ten feet they fall is 1d6 worth of gravity damage. If they are hit by the weight, they take 4d8 piercing damage, and another 1d8 bludgeoning from the weight itself, not to mention they weight will knock them free from the tunnel, and they take whatever falling damage is left. If there are multiple people in the tunnel, it is likely that one falling will cause a chain reaction to cause a massive pile up at the bottom of the chimney.
   The weight will stop with a jerk about 10 feet from the bottom of the tunnel, and then slowly crank back up to its usual position as the trap resets itself. Every player has about a 50% chance of triggering the trap, but if the person who tripped it can remember what the trigger stone felt like, and divulges this info to the rest of the party, that percentage drops to about 5%.
   Even if the PC’s think they can scramble up the tunnel while the trap is resetting itself are sorely mistaken, for if the trigger is tripped, no matter where the weight is, it will fall, and then start back up.
   

5. The Adventurers enter a round room about 35 feet or so in diameter. The room is filled with sand and there is nothing too special about it, except that the door leading out of the room is heavy steel with a wickedly tough lock that looks as though it needs a key. The ceiling, about 40 feet above, appears to be made of glass, and sitting on this glass sits a vast quantity of gold, or platinum, depending on how good a mood you’re in. Any yahoo will figure out the easiest way to get the cash down is to throw something at it like a rock or a boot. Even a bolt from a crossbow will shatter the glass. All must make a reflex save of 12 to negate falling glass damage. Once that’s done, it’s like Cinco de Mayo when the pinata’s meet its fate.
   However...
   The glass separated the room from about another five feet of altitude. Contained in the portion above the glass was a poisonous gas that begins to seep down to the players in about 1d2 rounds. Hopefully someone’s been working on the door, because the look is going to take about a DC of 45 or 50 to open, or about five rounds of continuous 20 to 25's to open the sucker. The poison takes a Fort save of 18 every round to keep from taking 1d10 Wis and/or Int damage. The door you came through can let you out, but the gas will keep coming out until you’re outside. The only way to separate yourself from it is to get the hell through the sealing steel door. If your players lose this and all pass out, maybe you should have them all wake up a few days later in nothing but their underwear. Maybe that will teach them to secure a way out before attempting a get-rich-quick scheme in the room. If you’re nice, maybe you can put the key to the door in with the gold or platinum that has fallen.

6. This is more of a trap to freak your PC’s out. Somewhere deep in a sadistic bastard’s dungeon,
   make it so that the only way to continue is through a long, sharp angled chute. The room it sits in is about twenty by twenty, and the lip of the chute sticks about three or feet up into the air in the center of the room, surrounded by sand bags.
   After two people have gone down, take that NPC that no one likes or you’ve been meaning to kill off and have him go next. The room the PC’s end up looks like the room they jumped down the chute in, the only difference is the chute is sticking out of a wall and not the floor. When the NPC hops down the others in the room hear a loud “ERRRRUM” and the NPC lands in the exit room in two halves length-wise. The PC’s will now freak out. The trick is that every third person that goes down causes a buzz saw to pop up in the middle of the slide about halfway down the chute. If the PC’s are smart, they will use the bags of sand to set the trigger off once they time it right.

7. This is more of a comical trap than anything that will cause damage. In a relatively short, narrow hallway, the floor is suddenly split by a five foot wide, ten foot across, and five foot deep pit. No problem. The first person who jumps across should have detected magic. About halfway across is an invisible wall. When the PC takes that running jump, he’ll hit that thing like a fly hitting a windshield, and then slowly slide down. The trick is to just climb down into the pit, walk under the wall, and climb up the other side. Hitting the wall with that running jump might cause 2d6 or so damage.

8. This is a good sadistic trap to put in a fighting arena. The room should be relatively large, and have lots of levels for fighting, with lots of cauldrons of burning tar for light, and other stuff. Put some heavy hitting enemies in the room, like some ogres or trolls. Ever some-odd feet, there is a five by five foot shaft. Falling in, or getting knocked into, rather, is a new level of pain all together. After good forty foot drop, the tunnel takes a 45 degree slope, and has protrusions in the surface much like a cheese grater. After so many feet of this (5d6 or 5d8 worth of damage) the player takes another vertical spill and lands in a forty by forty by five foot deep vat of salt water. This should probably just deal subdual damage, but it is very sadistic non the less. The only way he’s getting out is climb back out the way he went.

9. The players enter a narrow hallway with a small staircase leading up to a large, decorative door. A spot check should tell a PC that the walls are covered in a slick, oily liquid, and their are large scrape marks all along the wall. The door is made of stone, and has no apparent keyhole. It is also stuck, so a strong brute character will have to pull it open. The strength check to open is 22 or higher, depending on what level your pc's are at. When this Strength check succeeds, the PC's will be in for a surprise. The entire wall the door is set in completely slides towards the PC's and continues towards them on the greased walls, and will continue down the stairs after them.
   In the particular event I used this trap, I had put an open portcullis at the bottom of the stairs, and a pit to jump over. The Portcullis drops after so long, and if any of the PC's haven't cleared it, then they buy the farm. Or so they thought. The PC's who didn't make it fell into the pit, and the stone slab trapped door fell into the pit. Everyone assumed they had been squished. They had actually fallen down a funnel-like chute that dropped them into another part of the dungeon. It's a good way to split the party up if you need to.

10. The players enter a room with a 25-foot ceiling, and a floor of 30-feet by 20 feet. Two levers are on the far wall. As soon as they enter the room, both doors bolt down and the PCs are trapped. Closer inspection on the levers reveals two traps, Wall Trap and Ceiling Trap respectively. (The room's exit walls are 20 feet apart, while the wall-trap walls are 30 feet apart.)
    
    An inscription on the wall reads in Common: "Throw one switch and start the other." That is to say, if the players deactivate the Wall Trap, the Ceiling Trap automatically starts falling down to the floor, or vice-versa, where the two non-exit walls close in on each other. The doors do not open after a trap activates.
    
    In the room there are many random items (You can change this list as much as you like):
    -A Jar filled with beads
    -A large Beam (approx 25 feet long)
    -A chest containing sand
    -Any other random items you choose (the more there are, the harder it is to figure out the trap.)
    
    The Solution- put the beam straight-up from ceiling to floor. Then deactivate the wall trap. The ceiling trap will not fall down on the PCs, and the doors open.

11. This is a good trap for those hulking fighters who never appreciate their rogues. The PC's approach a door that looks like heavy, reinforced, and strong, however, it appears to be made from very soft wood, like Balsa, or some other kind. Their are no visible key holes, or anything to pick as far as locks go, but the door appears to be stuck. This whole door is trapped, however, so the Rogue will be able to disable it if he finds it to be trapped. However, most fighter/barbarian types will probably just try to smash on through. In doing so, the moment a momentous force (ie, axe, sword, fists, etc) strike the door, the door will explode, sending shards of wooden fragments into the PC's. The PC who struck the door in the first place will take 3d6 piercing damage, people within 5 feet take 2d6, and people within 10 feet take 1d6, and those outside of that get to point and laugh at the splinter covered party.

12. Our brave and fearless PCs come to a door that is heavy reinforced wood. It does not appeared to be locked. However, when the knob is turned and pulled, there is a lot of resistance, like someone on the other side is pulling on the door also. The person pulling the door should roll a strength check of about 15 or so, and then everyone must make a listen check to hear distant rumbling getting closer. The door opens freely now, and anyone can see that it opens to a ramp leading up, and that a rope attached to the other side of the door just pulled the support out from a large, round boulder, and now it's hurdling towards the PCs. This is really fun especially if they make a run for it, because the boulder take up all the space, so there's no getting around in, and in the campaign I ran when I put this in, the corridor leading to the door in the first place was really long, and on a slight grade, giving the boulder a never ending slope to role down.

13. This trap gave my PCs one hell of a time. It appears to be made completely out of glass and the PC's reflections show, so they can't see through it. Technically this is a mirror of opposition. The door only allows one person to go through at one time. When a PC goes through, he open the door, steps through and the door slams behind him. He has just entered a room facing the rest of his party. Wait for some "what the hell" 's to be murmured from the rest of the party but it goes like this.
    There is a party just like you, but of completely opposite alignments. When one PC goes through the door, their member of the bizarre party, goes through too, and finds himself facing what looks like his party, while the PC is on the other side looking at what he thinks is his own party, but is really the Bizarre party. But they don't know that, and it is almost guaranteed that multiple PC's will go through the door, go back through the door, and so on, until they finally realize they're dealing with their opposites, and must fight (now would be a good time to drop hints about the opposing party being evil, or good, whichever...) And now you must fight, but they're so damn mixed up, nobody knows who's who anymore.
    This is a very confusing trap, however, it works as a great encounter.

14. As the PCs move into this 50ft by 50ft room, they can see that there is a door on the opposing wall, and that the ceiling is 20ft high. The ceiling and floor of this chamber are made of smooth stone, and the door on the opposing wall is made out of a stone. About 1/4 of the way up the wall is a ring of green metal, about 6 inches wide. On the sides of both doors (the one the pcs entered and the one on the opposing wall) are 2 levers, and there are 2 others, 1 on each of the other walls. These are painted Red, Blue, Yellow, Orange, Purple, and Black. Also, they are set at the same level as the green metal ring, breaking the ring into several pieces along the wall.
    
    The placement of the levers doesn't actually matter, nor do the order of the colors. But as all of the PCs move into the room, both of the doors shut and seal themselves, becoming completely unopenable. Also, the ceiling begins to slowly fall down, at about 1ft per round. The PCs should begin to panic at this point, and will notice the levers. Pulling these will not cause the ceiling to stop or rise, it will actually cause one of the following effects:
    
    1: Causes the ceiling to fall faster, at 2ft per round instead of 1.
    2: Causes holes in the ceiling to open up.
    3: Causes spikes 1ft long to come out of the holes in 2
    4: Engulfs the lever puller in flames, dealing 2d6 fire damage.
    5: Gives the lever puller a short shock, dealing 1d6 electricity damage.
    6: Force effect pushes lever puller back 10ft.
    
    The answer to this trap is actually the ring of green metal. Touching the metal on each of the walls causes the ceiling to slop falling, and reverses the effects of 2 and 3 above. Running ones hands along the entire length of the metal ring causes the ceiling to return to normal height, along with unsealing the 2 doors.
    
    For increased Evilness, you can swap out the effects of the levers with more devastating events, such as causing the room to be slowly filled with water.

15. About halfway up a flight of steps is a false step. Its cover is made of brittle material, like disguised glass, and when stepped on with a certain weight shatters, and the PC's foot falls through. If he doesn't remove his foot carefully, and just pulls it on out, he'll realize his mistake, for there are spikes inside angled at about 45 degrees, so when his foot goes in, nothing happens, but when he tries to pull it out...have the PC take whatever damage you deem appropriate, but cut his base movement by half.

16. If anyone has ever seen "Raiders of the Lost Ark", when Dr. Jones is creeping through the booby trapped temple to take the golden idle head thing, the prized relic sits on a pedestal at the end of the room, with a long walk towards it with many tiles that looks like they could be pressure plates, and lots of holes in the way that look like they could fire darts. I pulled this on my PC's one time, and though it wasn't trapped at all ( I did that once they got to the prize) it sure as hell made them suspicious. One thing you can also do to this trap is make it unarmed when they walk across, but all are armed once the relic, idle, whatever is removed from its pedestal. Since your PC's thought it was safe to walk across the first time, maybe they'll think they can just mosey on out.

17. This is a spin to all you commonly used pit traps. It usually pays to have combat going on while you activate it.
    The PC's are fighting in a large circular rooms in a castle, fort, dungeon, HQ, etc, with big door leading in each cardinal direction. The room is about 50' in diameter and its full of rubbish. In the center of the room is a 20' diameter circle set into the floor. While fighting, if a lever is activate, whatever kind of trigger you want, opens the 20' area like a trap door. This is actually a garbage chute. After a good fall, they find why this is used as a garbage chute, because at the bottom is a huge gelatinous cube, err... cylinder, and he's sopping up the goods, which include falling PC's. Gravity ought to drive them pretty deep into the thing, and there's really only two ways to get a PC out of it. Kill it, or bungee jump into it and have the rest of the party haul you out (believe me, this option can work, I tried it once. It may sting a little though)

18. Its true, this is a trap I just use for comic relief. The PC's enter a room that appears to a have a rope dangling from the ceiling. upon further inspection, it appears to lead up through a hole in the ceiling into blackness. In a true case of curiosity killing the PC, if anyone attempts to climb the rope, their weight opens a trap door underneath them and snaps the rope. I usually put something good at the bottom of the pit, so the embarrassed PC at least has something to show for instead of just a bruised butt.

19. In a 10' wide hallway, make it pretty long, there appear to be pressure plates all along the floor. It looks as though who ever built the place didn't even go through the trouble of disguising them, and they are easily avoidable.
    However, to tests ones greedy habits, ever so many feet down the hall is a platinum lever in the up position. They look really appealing, and a successful appraise check will show they are worth about 500 GP each.
    They can break off with a strength check of 20, but if they miss the check there is a 50% chance they inadvertently threw the switch. Now it's time to see which of the part is the best sprinter.
    A heavy thud echoes through the hallway, and up the way they came, they can see three stone wheels, about the size of a modern day truck tire, rolling down the hallway, setting off all the pressure plates, sending up an array of traps from darts, arrows, gases, acids, flames, etc.

20. This is better for a higher level party. After the PC's have butchered their way through the dungeon, they reach the treasure room which sits in a round 50' diameter with a stepped platform in the center that is 20' in diameter and raised about 2 feet. Every five feet or so placed around the treasure platform is a stone pillar that is about 10' off the ground with a life sized stone statue of a warrior on each one (8 total). The Platform is covered with treasure, coins of all kind are scattered on the floor so thick, you can't even see the floor, weapon racks full of exotically designed and decorated weapons sit next to chests spilling with coins, jewels, gems and all kinds of art pieces. As the party begins to rummage through their new found treasure, the Statues spring to life, and will protect it at all costs.
    

21. This is a good trap for archers. The party enters a fairly good sized room, maybe 40X40 or 50x50 feet. The walls are made of hewn stone, with small circlets of metal inlayed into the wall. When approached, PCs in metal armor will "fell the slightest of sensations of being pulled toward the wall" The circles of metal are magnets, which do not appear to be very strong. However, unload a couple of monsters into the room, and the Archers of the party will just see how it will screw with their game. After firing a bolt or arrow, the projectile will travel about 20' and then begin to very toward one of the walls, striking anyone who happens to be in the flight path, even one of the own party mates.

22. As the PCs approached the house, there area was scattered with heavy stones. When the PCs came close to the rocks, the stones began to shake, and suddenly launched themselves at all wearing metal armor. The PCs thought that some sorcerer guard was playing tricks on them, but in fact the rocks were loadstones and placed around the residence to ward off intruders.

23. When the PCs fall into a pit, simple enough to put one in your dungeon, have them land on a chute, and begin sliding. Then divide them equally according to WEIGHT, and split them up via a fork in the chute or something. They are dropped out on two hard slabs of stone suspended by chains, and are about 20 feet away from each other, and below them is a vat of bubbling lava. In front of them is a platform that each party can jump onto to stay alive, assuming they make an appropriate check which I will leave to you to decide, however, they are on a balanced scale, and as soon as weight on one slab is taken off, or added ( if possible ) the other will begin to sink closer and closer to the lava.

24. The PC's enter a room that reveals quite a bit. When they enter the 30' wide X 60' long room, they notice immediately that the walls and ceiling are made of glass, and just outside is water, with an abundance of creatures and stuff floating around. Put some bad guys in the room who ain't too smart (ie orcs, goblins, whatever) and have them attack the party. Fighting will have to be done so carefully, because the glass will shatter on any impact.
    Once the glass is struck (easy caused by poorly aimed projectiles) water will start gushing into the room, and let some of the creatures in too. Try not to make a whole panel give out, but enough to make the PC's need to rush to the other door and hold their breath.

25. The PC's find a spot that looks promising for a search for traps (a door is best). When the rogue is done, he will have found that the trap is (flaming, acidic, gaseous, etc.) and is tripped by motion detection as soon as the door is open, which means he has to open the door to disarm it, but everyone in a 10' spread on either side of the door has to be really still. However, as soon as the rogue pops the door open, the party sees on the other side a really hungry, growling (owl-bear, dire bear, displacer beast, etc), and he lunges towards the party. If the party flees they'll set off the trap, but the hungry beast will set it off anyway...what to do?

26. This trap works best on low level henchman, like kobolds or goblins, or something of the like. They are all wearing these vibrant red medallions that the party will truly want ( because they're greedy, duh) but what they do not realize that these kabolds are fanatics and will stop at nothing to prevent the party from taking another step in their dungeon. When the fight begins to sway in favor of the party, the kobolds will lead a charge into the party, all striking their medallions before they hit. The medallions explode, dealing
    2d6 damage to everyone withing 5' of the explosion, which doesn't sound like much, but when you have a few dozen go off around the PC's, that's a lot of damage. Another thing, one explosion will trigger the others, so even the dead kobold's charges go off too.

27. This is a good trap for the meathead of the party (as so many of these traps seem to target) But a heavy door in the wall of the castle your PC's are traveling through that leads to...nowhere. The door is set into the wall, and is unopenable (word??) When the hefty dude (or dudette) of the party tries to open it the old fashioned way, via a foot through the thing, the door gives way, and the PC needs to role a balance check, or fall out the side of the castle wall. Works particularly well on towers that are pretty dern high:

28. This trap works particularly well when your PC's have ran out of food and are near eating thier boots. Deep in enemy territory, they come across a large, wide crevace that runs pretty deep, with steep slopes on either side. The surface they stant in is thick with foliage and lots of little cavelings and nooks for shelter, and better yet, trees with fruit on them. The starving party will want these immediatly, but make them roll a spot check when they see the fruit to begin with. If they made the spot check (DC 15-18) they see that the fruit appears to be pineapples.
    This SHOULD make them think. pineapples don't grow on trees, something is awry, but in my campaign, they were to hungry to ask questions and shook the tree until the fruit came down.
    This is a booby trap that the enemy has set up in this small grove. The Pineapples are actually bombs (pineapple grenades...get it!) and when they are shaken loose, and hit the ground, or the PC's, they explode. In my campaign, I actually made these like flash-bangs, where the PC was blinded and deafened for 2d6 rounds with a Reflex save of 15 to cut rounds blind and deaf in half, rounding up. This doubled as an alarm, and enemy troops heard the comotion, and a fight insued. The fact they were on top of the ridge, and above the PC's didn't hepl them any either.

29. This is a reverse drawbridge, and by that, I mean instead of it raising up, and keeping you from going up the incline, it drops to a 45 degree and and dumps you into the moat, cavern, etc. I pulled this on my PC's one time when they were raiding a keep that was set up on a sliver of cliff off a platue, so the only way to get to the keep, other than the bridge, was to scale down the two hundred foot cliff face and then back up. The PC's and their NPC's were already fighting on the bridge, when they saw the men in the gate house go for the winch. They assumed that since they were already on the bridge, they either couldn't lift the bridge due to the weight of the people one it, or the rising bridge would just knock them into the fort. What they didn't expect was for the bridge to just drop, and dump everybody down into the gulch, killing all the NPC's and two PC's (200 foot falls tend to do that) The PC's can roll a reflex of about 13 to hold onto something, and then what do they do? My PC's tried to climb back up, under fire from archers on the crenals of the keep. They didn't like me too much after words...

30. The trap includes a 30'X30' foot room with a 10'x10' shaft leading up through the ceiling, a thick, strong, knotted rope dangling down through the shaft allows the PC's easy access to the top. But only if they do it right.
    For the rope isn't tied down to anything per se, rather it is tied to a 500 lb weight that sits on the ledge at the top 150' above, and a pulley in the ceiling threads the rope from the weight to the PC's below. When one PC gets on, nothing happens. If two get on, if they don't go over the 500 lb limit, then nothing still should happen. However, once they cross that 500 lb range, the weight slides off the ledge and pulls a 1000 lb weight off. Now it gets good.
    Whoever's clinging to the rope needs to role a strength (or dex check, which ever you prefer) to keep a hold of the rope as the weight jerks the $*&% out of it. The check should be relatively high, it is 1500 lbs we're talking about here. However fails falls off, and takes the appropriate falling damage, and the others who are left on the rope are now taken for a ride as the weight sails down, they shoot up. When the PC's pass the weight coming down, they each must roll a percent check to see if they get clipped by it (25-50 % chance) Which incurrs about 3d8 points of bludgeoning damage and perhaps another chance to fall off.
    Whoever is standing in the room below must make a reflex save to avoid the weight when it crashes into the floor, or (check of 13-16, 5d8 Blud. Dmg.)
    Now the yahoo's still holding onto the rope will now kiss the ceiling and the pulley as the others below are diving out of the way. This should be another 3-6 d8's worth of damage, plus the loss of use of one's hand or maybe a few missing fingers from eating the pulley.
    Then they must roll to keep hold again, and if they fail, they again take the appropriate falling damage. Or you could just do what I did and have the weight break in half one it his the ground, and now that it weighed less than the PC's, they plummit back down after kissing the sky. Mind you, they again could get clipped as the weight goes back up.