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This is actually something I used in a previous game I ran around a year or so ago.
The idea is this: How do you create traps that are obviously visible but still create a challenge for the party?
For example:
Say you want a "trap" that involves four blades swinging back and forth over a narrow bridge (with no hand-rails).
This is obviously a trap, but it isn't surprising - you can clearly see the narrow bridge and swinging blades. Passing a perception check wouldn't help "find" this trap. Likewise, there's nothing to disable - you can't "disable" a narrow bridge, and you can't "disable" swinging blades when you can't reach the mechanism that controls them.
Or, to use another example, the party is at the bottom of a long ramp. At the top is a device which rolls boulders down the ramp at a set, predictable rate. The party can clearly see the rocks and predict the rate, but their movement speed is also not enough to reach the top without getting hit by a boulder. Again, nothing to perceive - they can clearly see the rocks - and nothing to disable - at least not at the bottom of the ramp.
My Variant works like this: Replace the Perception and Disable DCs with other skills that can help overcome the trap.
In the case of the swinging blades over a narrow bridge trap example above, I'd create the blades and bridge like a swinging axe + pit trap. Rather than a Ref save, the Axe would get a Bull Rush attempt on anyone it hits, with failure meaning they fall into the "pit" - ie off the bridge. So far so simple.
For the skill checks, I replace the Perception DC with an Acrobatics DC. A character can slip past the blades without ever being the subject of an attack roll (and thus no bull rush) if they pass a DC 25 acrobatics check.
Alternatively, a character can "disable" the trap with a DC 20 strength check and either a blunt weapon or shield. Basically, they step in the way and "catch" the blade against a blunt object. If they pass the Strength check, the blade breaks. If they fail, they are hit and bull-rushed as normal (the attack auto-succeeds because they stepped in front of it).
For the rolling rock trap, rather than a Perception DC, the party can make a Knowledge (engineering) check to predict the timing of the rocks, allowing them to time their movements to avoid the rocks. Alternatively, a PC could make a climb check to climb along the side of the ramp outside the range of the rocks.
In addition to mixing things up, this is particularly good for parties with no "trap finder" classes. Plus, while the occasional "gotcha" trap is fun, having these more environmental challenge style traps mixes it up.
Anyway, my group enjoyed them, and I thought others might as well.
Dot
I like it
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Thanks for the interest!
Here are a couple of the traps I used in the aforementioned campaign.
As can be seen from the calculations below, I limited CR calculations to only two skills even if I used three or four. Also, as will become obvious rather rapidly, in that particular game, Acrobatics and Knowledge (engineering) were my go-to skills for mechanical traps. I would throw in Knowledge (arcana) for traps with a magical component. Overall, though, I treated all traps as mechanical traps when possible since those are much easier to calculate for.
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Rotating Fire Trap CR 7
Acrobatics DC 21, Knowledge (engineering) DC 21
These rotating jets of flame make navigating narrow areas difficult. The flame jets are easily visible and pass through certain squares regularly. Any creature passing through the 10 ft. radius may roll an acrobatics check to roll beneath the fire or a Knowledge (engineering) check to walk carefully with the rotation between jets of flame. If a target fails their chosen check (or chooses not to make one) then they take 6d6 fire damage while passing through the radius (Ref 21 for half).
CR calculation: CR 0 +1 (acro DC 21), +1 (know DC 21), +1 (ref DC 21), +4 (average damage 21, x2 for multiple targets) = CR 7
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Rolling Rock Trap CR 7
Acrobatics DC 25, Climb DC 25, Knowledge (engineering) DC 21
The main hall contains a stairway with a curved divot that the party has to ascend to exit the room. Every round, a stone sphere is rolled down the divot before falling into a hole.
A character can climb up the side of the ramp to attempt to avoid the trap entirely. Alternatively, a character can make use of a series of small alcoves in the wall beside the ramp. To do so, a character can either make a Knowledge (engineering) check (DC 21) to predict when the rock will arrive or an Acrobatics check (DC 25) to leap into them when they see the rock coming.
Any creature that fails the climb check takes normal falling damage (2d6 for 20 ft.). Any creature that fails its choice of an acrobatics or knowledge (engineering) check is hit by the rock, taking 4d6+6 blunt damage (ref for half). A creature that takes damage from the rock is also subject to a Bull rush attempt (the rock as an effective CMB of +10). If the rock overcomes the target's CMD, they are knocked back down to the bottom of the ramp and must attempt to pass the trap again. Those who are not bull-rushed can continue up the ramp, reaching the top before the next rock arrives.
CR calculation: CR 0 + 1 (acro/climb 25), +1 (know 21), +1 (ref DC 25), +0 (+10 CMB), +4 (average damage 20, x2 multiple targets) = CR 7
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Swinging Blades over Narrow Bridge Trap CR 10
Acrobatics DC 25, Knowledge (engineering) DC 25, Strength Check DC 20, Climb DC 30)
This room consists of a narrow (5 ft wide) bridge spanning the third floor of the building, the floor beneath two stories (or 40 ft.) below. Four blades swing across the bridge at regular intervals. A creature crossing the bridge may make either a knowledge (engineering) check (DC 25) to carefully time their movements between the blades or an Acrobatics check (DC 25) to quickly dodge between them. A character who fails either check is subject to the blade attacks. Each of the four blades attacks for +11 to hit; each successful hit deals 1d8+1 damage. In addition, any creature that takes damage from the blades is subject to a Bull Rush (CMB +11). Those that fail fall from the narrow bridge, taking 4d6 falling damage.
A character can choose to make neither check and can instead attempt a Strength Check to stop the blades. Doing so requires a blunt object (such as a two-handed weapon, a shield, or a large rock) and a DC 20 Strength check to stop the blade. This causes the mechanism that moves the blades to strip its gears and stops the blades from moving, rendering them harmless.
Alternatively, a character can bypass the blades entirely by hanging off the side of the bridge and slowly climbing sideways to the other side. This process is very difficult, requiring a Climb check DC 30 to succeed. Failure by 5 or more results in the character falling (and taking 4d6 falling damage).
CR calculation: CR 0 + 1 (acro 25), +1 (know 25), +1 (+11 to hit), + 7 (average damage 36, x2 multiple targets) = CR 10
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Floor Spike Trap CR 11
Acrobatics DC 25, Knowledge (arcana) DC 25
A patch of the floor has spikes that extend and retract in a regular pattern. A creature can dash over the spikes while they are lowered easily enough, but the difficulty is timing since one must also wait for the next set to lower, meaning that one has to get the timing just right.
A creature moving over the spikes can make either a knowledge (arcana) check (DC 25) to predict when the spikes will extend or an acrobatics check (DC 25) to avoid them when they do so.
A creature that fails their chosen check is attacked by 4 spikes with a +11 to hit and takes 1d8+6 damage per successful hit (reflex DC 25 for half).
CR calculation: CR 0 +1 (acro DC 25), +1 (know DC 25), +1 (ref DC 25), +8 (average damage 42, x2 for multiple targets) = CR 11
This is a great idea thanks for posting.
Dotting
Favorited.
I love anything that allows the players to come up with creative solutions, especially at low levels when spells are rare and equipment is useful. (I would totally allow players to use a shield as a portable rest stop on the spikes, or push some stones to block the fire gout path, or jam an adamantium piton in the boulder ramp entryway).
I have planned out some similar obstacles myself for a gauntlet style event, and I hesitate to call them, or these true traps. Scrapper may be right in calling them hazards more than anything.
Favorited.
This is a great idea thanks for posting.
Dotting
Thank you!
I would classify these as Hazards rather than Traps,
Scrapper may be right in calling them hazards more than anything.
Well, Hazards don't have a table for calculating CRs. Traps do. Call em whatever you like, but one would follow trap mechanics for building them, except as noted above.