CR of homebrew trap

[Roninblack]

So I'm designing a trick dungeon that upon entering the boss room the entire dungeon will seal shut and lanterns will light with the intent to suffocate out the party.

The only living creature in the dungeon is an ooze, the boss is an animated object, so the denizens shouldn't really be at risk.

My napkin math and rounding gives them 30 min. To find the secret door to move on if pannicked, or an hour if calm.

I figured I'd set it similar to a portcullis trap, and the trigger is several hundred feet away, so it's not a falling stone trap.

What CR would you give this?

[gijoemike]

Level of party? Teleport and D Door shut this trap down completely. I assume a very low level party.

What is the DC to find the hidden door? Are there clues to its location elsewhere in the complex?

How difficult is it to just beat down the first seal at the entrance?

So not just a save or die trap this is an entire PARTY save or die? Its not a save, its a skill check that most characters cannot take as class skills.

Is it obvious they are in a ticking down death trap? I mean as a PC if I walk into a room, I hear a door slam somewhere behind me and a bunch of lights come on I don't imminently assume "I've got 30 mins to live!"

How big is the dungeon? It is 6 full seconds ( full round) to search a 5x5 square. A 30" by 30" room would take a single person 36 rounds to search. So 600 squares can be searched by each party member in an hour, given 1 round per square. Assuming 6 person party, 4 of whom have a search bonus results in 2400 squares, but without any movement or fights. But lets be honest those PC will be assisting the rogue so it is much more likely with movement to be closer to 1200 to 1500. And that assumes an hour. There is a real chance your pcs never search the square with the exit. That means they die without getting a roll.

While there is a living ooze how many other fights and traps are in the dungeon?

OH the trigger is several 100" away. This indicates a fairly large dungeon. So the exit is somewhere in a massive complex, locked behind a 1 time roll skill check (due to time constraints). And that one roll kills the entire party?

As a not obvious single save death trap for the whole party, multiple fights to distract them, and few who can reasonable search for the trap... I would rate this as stupid high CR. To the point don't do it.

A portcullis trap is a terrible comparison or starting point. The falling stone trap is much much closer. This is really a crushing cage trap (CR 11), with a locked portcullis on both ends of the hallway. A normal crushing cage trap has an obvious exit. This trap doesn't And there are monsters in the cage with you. Adding all that together is like a CR 16(according the super terrible trap cr rules). But even then that assumes a limited space to search. So keep that in mind.

People don't realize that stacking traps together like this pushes CR through the roof. If the PC's cannot encounter the components separately then they aren't calculated as one trap, then a separate trap, then a 3rd but separate trap. It is actually a massive very deadly trap.

[Roninblack]

I guess I should have included that this is theoretical. it's a test to see how hard a dungeon can be made while still being beatable (and I realize this is a stretch) with enough xp to take a 5 man party from lvl 1 to lvl 2 and award them enough gp to keep up wbl the same using only 1000gp or less items and cr 3 or less challenges. I'm trying to make sure the trap abides by these guidelines. I'm trying to stay within the SRD and a couple of my players who wanna be gms are doing it and I wanted to provide an example.

So if it helps its a spiral with 6 20x20 rooms, and 7 10 ft by 50 ft hallways.
There are a pair of fake doors with a poison needle trap, and a dart fussilade trap, and an animated sarcophagus as the only other fight.

If my numbers are close there's 94200 liters of Air in a dungeon of those dimensions and being kind, they go through 300 liters of air a minute, (900 but they only benefit 25%)

Standard secret door is dc 20?

The very first hallway has a pit trap with the ooze in the bottom, and that's where the secret door is al la tomb of horrors.

So yes no d door or telephone, 1st level party, I figured 10×10 stone block seal. Triggers when the sarcophagus gets off the trigger. The lanterns are no effect but to signify that something changed and scare the party with a timer, and because they couldn't be moved or lit, hopefully it is a decent indicator.

*edit for waspishness and detail

[Jack_Simth]

So I'm designing a trick dungeon that upon entering the boss room the entire dungeon will seal shut and lanterns will light with the intent to suffocate out the party.

The only living creature in the dungeon is an ooze, the boss is an animated object, so the denizens shouldn't really be at risk.

My napkin math and rounding gives them 30 min. To find the secret door to move on if pannicked, or an hour if calm.

I figured I'd set it similar to a portcullis trap, and the trigger is several hundred feet away, so it's not a falling stone trap.

What CR would you give this?
First, it's Slow Suffocation (https://www.d20srd.org/srd/environment.htm#suffocation) once they're "out" of air. Which, at 1d6 per 15 minutes, is actually quite some time. OK, that's pretty quick for a 1st level party. One or two instances will likely knock out the tinderbox, 2-3 for the trapmonkey, 3-4 for the first-aid kit, and 3-6 for the meatshield.

As noted, the Dimension Door Spell shuts this down hard. So a "balanced" party of 10th level or so should barely notice (a balanced party of 7th level or higher could get out trivially if they happen to prepare the right spells, but past 10th Dimension Door or better in someone's hands is pretty much a given). There's also a few items that do so - a Bottle of Air or a Necklace of Adaptation to name two.


As for the CR, let's see what the guidelines (https://www.d20srd.org/srd/traps.htm#designingATrap) say.
1) It's multiple targets, never miss (+0 CR)
2) Onset Delay of more than 3 rounds (-1 CR)
3) You'll need to assign a search DC (from -1 to +2 to the CR).
4) You'll need to assign a disable device DC (from -1 to +2 to the CR).
5) And the effect is damage over time (it's how slow suffocation works).

I'm going to guess you don't want search or disable device to carry the day. So that's +4 there (DC 30 or higher for both). So before we get into the damage, it's a CR 3 mechanical trap. 1d6 per 15 minutes for the entire party (and nonlethal to boot). There's no end condition (other than leaving, though), which makes this aspect hard to ID.

If we largely assume that the party will clear out their path on the way into the boss room (and thus, have a mostly clear path back out), how long will it take for them to get close enough to the main exit door to start full attacking it? It's 6*20 (rooms) + 50 * 7 (hallways) = 470 feet away. At a simple walk, a dwarf in full plate will get that in 24 rounds. 2.5 minutes.

If there's fights along the way back (which seems odd if it's triggered in the boss room in an effectively linear dungeon!) this time goes up, but the real kicker is "You can't stop to rest up" when the standard D&D paradigm assumes four CR = level fights per day between rests (more if lower CR, less if higher).

[Roninblack]

First, it's Slow Suffocation (https://www.d20srd.org/srd/environment.htm#suffocation) once they're "out" of air. Which, at 1d6 per 15 minutes, is actually quite some time.

As for the CR, let's see what the guidelines (https://www.d20srd.org/srd/traps.htm#designingATrap) say.
1) It's multiple targets, never miss (+0 CR)
2) Onset Delay of more than 3 rounds (-1 CR)
3) You'll need to assign a search DC (from -1 to +2 to the CR).
4) You'll need to assign a disable device DC (from -1 to +2 to the CR).
5) And the effect is damage over time (it's how slow suffocation works).

I'm going to guess you don't want search or disable device to carry the day. So that's +4 there (DC 30 or higher for both). So before we get into the damage, it's a CR 3 mechanical trap. 1d6 per 15 minutes for the entire party (and nonlethal to boot). There's no end condition (other than leaving, though), which makes this aspect hard to ID.
I didn't know about slow suffocation, so thats very helpful. Actually DC 20 seems more than reasonable for a 1st level party, so that's fine. I also am estimating a CR 3 trap, because it is very similar to a water room trap but affects a much larger area, and takes much longer.

Edit: Using the slow suffocation rules there are 516 hours of air in here for 1 medium creature... So I need 511 lamps in this freaking place to give a party of 5 1 hour to get out!


If we largely assume that the party will clear out their path on the way into the boss room (and thus, have a mostly clear path back out), how long will it take for them to get close enough to the main exit door to start full attacking it? It's 6*20 (rooms) + 50 * 7 (hallways) = 470 feet away. At a simple walk, a dwarf in full plate will get that in 24 rounds. 2.5 minutes.

If there's fights along the way back (which seems odd if it's triggered in the boss room in an effectively linear dungeon!) this time goes up, but the real kicker is "You can't stop to rest up" when the standard D&D paradigm assumes four CR = level fights per day between rests (more if lower CR, less if higher).

Based on my rough count and pathing, it's 450 ft from boss room to entrance with a total of 30 ft worth of stairs and a 60 ft change in altitude. so your numbers for assumptions are pretty good.
I figured a 5 ft thick block of stone should be reasonably difficult to break as it amounts to 180 hp with hardness 8.

[Jack_Simth]

I didn't know about slow suffocation, so thats very helpful. Actually DC 20 seems more than reasonable for a 1st level party, so that's fine. I also am estimating a CR 3 trap, because it is very similar to a water room trap but affects a much larger area, and takes much longer.

Edit: Using the slow suffocation rules there are 516 hours of air in here for 1 medium creature... So I need 511 lamps in this freaking place to give a party of 5 1 hour to get out!


Based on my rough count and pathing, it's 450 ft from boss room to entrance with a total of 30 ft worth of stairs and a 60 ft change in altitude. so your numbers for assumptions are pretty good.
I figured a 5 ft thick block of stone should be reasonably difficult to break as it amounts to 180 hp with hardness 8.

OK. Assuming a Greataxe wielding Barbarian-1 with a non-rage Strength of 16 and power attack, 1d12 (base)+4 (3*1.5, round down) +2 (power attack: another +1 in Pathfinder, due to how power attack works), half damage to objects before hardness, they deal one point of actual damage to the wall when they roll max (12+4+2=18 ; 18/2=9 ; 9-8=1). Assuming a 90% hit rate vs. a wall, that's an average of 0.075 actual damage per round = 2,400 rounds to dig through (about 4 hours; 3.6 hours if you can auto-hit walls, which I think you actually can, but I'd need to look it up). Rage won't last long enough to matter.

Which means they're all toast if they don't think to search the specific spot where the secret passage happens to be.
Beware: This is a puzzle trap where the solution is ultimately "Guess what the DM is thinking", and is liable to TPK most 1st level parties if it goes off.

Note: Might not if they have a reasonable chance to prevent it from ever triggering in the first place (e.g., if they search the entrance on the way in, they should reasonably be able to ID that the door closes, and disable that aspect, as the door is part of the trap).

[Roninblack]

I had the same thought about closing the door, but I think your math is a little off where did the half damage before hardness come from?
I believe they do auto hit the wall, dealing 1d12+4 because of 2 handed, +2 from power attack for 2 handed, or 1d12+6 an average of 12.5 per round. Minus 8 points for hardness the barbarian breaks through on average in 40 rounds, or 4 minutes.

[One Step Two]

Edit: Using the slow suffocation rules there are 516 hours of air in here for 1 medium creature... So I need 511 lamps in this freaking place to give a party of 5 1 hour to get out!

You can handwave the number of torches, a large bonfire, or brazier could easily account for the consumption of oxygen. You can also give context clues to what the party will expect, describing the dungeon as having stagnant air, no feeling of wind, and the underlying taste of ashes in the air.

The half damage vs objects is only for Fire, Electricity and Ranged weapons from memory.

[Jack_Simth]

You can handwave the number of torches, a large bonfire, or brazier could easily account for the consumption of oxygen. You can also give context clues to what the party will expect, describing the dungeon as having stagnant air, no feeling of wind, and the underlying taste of ashes in the air.

The half damage vs objects is only for Fire, Electricity and Ranged weapons from memory.

Actively looking for it now, I'm not finding the half damage vs. objects in the general case; looks like I was mistaken. That does change the math.

Same Greataxe wielding barbarian's damage will start on a 3: 3+4+2=9; 9-8=1. Doing a math on all the d12 rolls... average of 4.58333... per hit. 180 hp means an average of 39.272727... hits required. And a full round action to line up the shot (and at 1st, no reason not to) is a never miss circumstance (found it while looking for the half damage thing: Here (https://www.d20srd.org/srd/exploration.htm#breakingAndEntering): "Furthermore, if you take a full-round action to line up a shot, you get an automatic hit with a melee weapon"). So four minutes to demolish the exit block.

That makes it a bit better, as long as they figure out they need to go.

[Zombimode]

Level of party? Teleport and D Door shut this trap down completely. I assume a very low level party.

1. You need characters with those abilities in the party - not every will have these.
2. These need to be available at that time.
3. Then the relevant ability will be spend escaping this trap - and thus won't be available for any other application. Depending on the circumstances this could be more relevant as any non-lethal HP damage ever could.

[Roninblack]

Alright, so all this given I think we've established that it's far more survivable than originally believed, does CR 3 still seem right?

[Jack_Simth]

Alright, so all this given I think we've established that it's far more survivable than originally believed, does CR 3 still seem right?

It's... not even going to consume any resources. It can be brute-forced in less than ten minutes by the party meatshield at basically no risk, provided the situation is clear. So... CR 1 at best.