The Pathfinder spell Unseen Engineers has the following description:
You conjure an invisible team of tiny engineers to construct a trap at alarming speed. Originating at your location, the team must remain within range of you or the spell ends. The engineers construct a mechanical trap of your choice. Construction takes a number of rounds equal to the trap’s challenge rating. The engineers must have the materials available. At the end of the construction time, use your Craft(traps) skill with a +5 bonus to determine the success of their work. If the engineers succeed, the trap is complete and the spell ends. If they fail, the materials are deposited at that location and the spell ends. If the spell’s duration ends before the trap is complete, the engineers automatically fail.
The engineers move at your base speed and can carry only materials required in the construction of the desired trap. They can’t attack in any way or be killed, and dissipate if they take 12 points of damage from area attacks (they get no saves against attacks).
What form must these required materials be in, and does this change for magical traps?
(Of course, this is ultimately up to my discretion as GM.)
The caster needs only the raw materials (e.g. wood, stone, earth, metal, and/or specific poisons), and the Unseen Engineers do the crafting magically-fast.
- A Barbed Wire trap would only require raw metal (or metal shrapnel), and the Unseen Engineers would make Barbed Wire out of it and place it as directed.
- A Bull Rush Statue trap would need the stone/metal to make the statues.
- An Acid Arrow Trap would require [metal? wood? acid?], and the Unseen Servants would craft the arrows and place them as directed.
Advantage: This interpretation circumvents awkwardness/complications related to magical items and extremely simple traps. (How would the engineers build a pit for a pit trap? Would they need to have a scroll or potion to create a magical trap, or would the caster be the one to cast a spell for that trap?)
Disadvantage: It seems too easy to make complex traps. Some items seem too complicated to be made this way.
The Unseen Engineers serve only to move things into place. The caster needs specific, pre-made materials, such as....
- A pre-existing pit for a Pit Trap?
- Pre-made poisoned darts for a Poisoned Dart Trap?
- Pre-made barbed wire for a Barbed Wire trap?
- A pre-made portcullis for a Falling Portcullis trap?
Advantage: This makes it more realistic: the Unseen Engineers move stuff, which is why a bunch of them do it so quickly. Disadvantage: It begs the question of how to make more complicated things, like magical traps or traps with lots of gears, glues, etc.