Lets steal from spellcasting. Because why not.
- There are 4 levels of traps.
- You gain access to a new level of trap at 3/7/13/19. Or maybe 3/6/11/16 to make it "1/5th your level, round up"?
- There is Preparing, Setting and Triggering traps.
- You Prepare traps during rests.
- Traps can be "upcast" for extra damage and sometimes effects.
- Setting a trap over 10 minutes generates an "upcast" type effect.
- Setting a trap as an action doesn't.
- Monsters can trigger a trap. You can also manually trigger a trap as an action.
We now need a few traps of each level. And stealing from spells, lets make them hyper-specific. These are specific traps invented by specific trapmakers that you are deploying.
Names are easy to come by: Lidda, Jarlaxle, Artemis, Tasslehoff, Cale, Lupin, Mirt, Templar, Gord, Cyric
Random traps:
Tripwire that fires a Dart that puts you to sleep
Noose that grabs you and turns you upside down
Triggered explosion if you enter an area
Spray of Gooey Acid, that you then set on Fire
A bear-strength leg-grabber with teeth
Mimic Glue that sticks you to the ground or other surface
A flame thrower set off by noise
A spring that blashes you into a wall or ceiling
Rust monster dust shot into the air by a whoopie cushion
Basic caltrops that stick in your feet
Spring-loaded blades that snicker-snak
A rope that shoves the last creature to enter into a rope-trick pocket, ejecting the previous
An anti-magic region
Mummified illithid head that shoots a psychic stun attack, fueled by the spellcasting that triggers it
Tarrasque bone that regenerates rapidly to a certain size, crushing people
Bellows that blows air through the vocal cords of a harpy, charming the triggerer
...
We can have the most mundane traps be level 1. Caltrops, Ball Bearings, Oil + Flame spray, Acid Splash.
Level 2 can be more complex mechanical stuff. Springs, Foot traps, cages, snicker-snak blades, powder kegs.
Level 3 can start getting exotic. Mimic glue, rust monster dust, gelatenous cube, harpy vocal chords, carrion crawler tentacles, etc. Complex and uses magical ingredients.
Level 4 is high end. Illithid heads, Tarrasque bone, anti-magic, rope-trick-trap, demon blood, etc. Heavily magical.
Traps can have a materials cost. Often the cost is split in materials and per-use costs, with per-use being much lower. This explains "where did you get a tarrasque bone fragment to do that trap" - you paid for it.
...
By making it (action to set up) (action to trigger) we get the basic action economy.
(action to set up) (automatic trigger) rewards cleverness and teamwork. In some cases you can deploy the trap under someone's feet, however, and this becomes the default for them.
(10 minute set up) then (action to trigger) gives the trap maker a bonus, both saving the set up and giving a larger payoff. We can limit how many 10 minute set up traps the player can deploy (make them only last 10 minutes without maintenance, so you only get 1 for an encounter, for example).
(10 minute set up) then (automatic trigger) is even more efficient than the above.
(long rest set up) is another option, more akin to making a magic item. It costs a lot more in materials and time to make a trap that can not be babysat.
