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Difference between revisions of "v0.31:Trap design"
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==Introduction== | ==Introduction== | ||
| − | Simple one-tile {{l|trap|trap}}s* are just that - they exist only on their own tile, trigger themselves when a target walks onto that one tile, and affect only that one tile. Complex traps and automation rely on linking {{l|door|door}}s, | + | Simple one-tile {{l|trap|trap}}s* are just that - they exist only on their own tile, trigger themselves when a target walks onto that one tile, and affect only that one tile. Complex traps and automation rely on linking {{l|door|door}}s, {{l|hatch}}es, {{l|floodgate|floodgate}}s, {{l|bridge|bridge}}s and mechanic's traps to {{l|lever|lever}}s or {{l|pressure plate|pressure plate}}s, along with {{l|machinery|machinery}} to provide the power to run some of the more diabolical designs. When the trigger is activated, it sends a {{l|lever|signal}} to the linked device. That signal is not always as simple as "do it now", but it's specifically either to "open" or to "close". By manipulating what does what and when, and what follows from that, impressive results can be achieved. |
:''(* specifically, the {{l|Trap#Stone-fall_Trap|stone-fall trap}}, {{l|Trap#Weapon_Trap|weapon trap}}, and {{l|Trap#Cage_Trap|cage trap}}.)'' | :''(* specifically, the {{l|Trap#Stone-fall_Trap|stone-fall trap}}, {{l|Trap#Weapon_Trap|weapon trap}}, and {{l|Trap#Cage_Trap|cage trap}}.)'' | ||
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===Cage trap=== | ===Cage trap=== | ||
| − | :A very powerful type of trap. Maybe even too powerful - currently, even a wooden or glass {{l|cage|cage}} can hold indefinitely any creature, even trolls and megabeasts. A cage trap never fails. Use cage traps as your outermost traps to catch the occasional wandering animal, or angry wounded {{l|elephant|elephant}} or {{l|unicorn|unicorn}}, or even {{l|zombie|zombie}}s. Caged animals and enemies will be safely brought to any animal stockpiles you have, but may escape later if you are not careful. For more information, see | + | :A very powerful type of trap. Maybe even too powerful - currently, even a wooden or glass {{l|cage|cage}} can hold indefinitely any creature, even trolls and megabeasts. A cage trap never fails. Use cage traps as your outermost traps to catch the occasional wandering animal, or angry wounded {{l|elephant|elephant}} or {{l|unicorn|unicorn}}, or even {{l|zombie|zombie}}s. Caged animals and enemies will be safely brought to any animal stockpiles you have, but may escape later if you are not careful. For more information, see {{l|captured creatures}}. |
==Linked traps== | ==Linked traps== | ||
These traps require a trigger such as a {{l|pressure plate|pressure plate}} or {{l|lever|lever}}. They will require at least three {{l|mechanisms|mechanisms}}, one for the trigger and two to create the link. The trigger can be located any distance from the trap, typically close for a pressure plate or far away for a lever. | These traps require a trigger such as a {{l|pressure plate|pressure plate}} or {{l|lever|lever}}. They will require at least three {{l|mechanisms|mechanisms}}, one for the trigger and two to create the link. The trigger can be located any distance from the trap, typically close for a pressure plate or far away for a lever. | ||
| − | For a system that repeatedly activates automatically and regularly regardless of enemies, see | + | For a system that repeatedly activates automatically and regularly regardless of enemies, see {{l|Repeater}}. |
===Menacing spikes=== | ===Menacing spikes=== | ||
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===Dropping the Hammer=== | ===Dropping the Hammer=== | ||
| − | Lowering {{l|drawbridge|drawbridge}}s on invaders will {{l|dwarven atom smasher|crush}} them into nothingness. Known as the 'Dwarven Atom Smasher', bridges will destroy most things with some notable exceptions including | + | Lowering {{l|drawbridge|drawbridge}}s on invaders will {{l|dwarven atom smasher|crush}} them into nothingness. Known as the 'Dwarven Atom Smasher', bridges will destroy most things with some notable exceptions including {{l|wagon}}s and {{l|elephant}}s, who will not only survive unscathed but also destroy the bridge. |
| − | Try replacing the side wall of a part of your main entrance with a drawbridge, big enough so it spans the whole hallway. To prevent enemies with the {{l|Creature_Tokens|[BUILDINGDESTROYER]}} tag from wrecking it, you can dig a | + | Try replacing the side wall of a part of your main entrance with a drawbridge, big enough so it spans the whole hallway. To prevent enemies with the {{l|Creature_Tokens|[BUILDINGDESTROYER]}} tag from wrecking it, you can dig a {{l|channel}} in front of it for protection while it's raised. Link the drawbridge to a {{l|lever|trigger}}, and whenever you feel like it activate the trap. This can be done with minimal effort and used to smash {{l|invader}}s, unwanted {{l|immigrants}}, bothersome {{l|nobles}}, or simply to destroy your garbage. |
===Intentional cave-in=== | ===Intentional cave-in=== | ||
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A flooding room trap combined with an unextinguishable burning Lignite bin. The water will evaporate on the bin's tile, causing the water from the surrounding tiles to move to it, which then get evaporated as well. The water will also push the invaders onto the fire, causing them to burn to death... in a flooding chamber. | A flooding room trap combined with an unextinguishable burning Lignite bin. The water will evaporate on the bin's tile, causing the water from the surrounding tiles to move to it, which then get evaporated as well. The water will also push the invaders onto the fire, causing them to burn to death... in a flooding chamber. | ||
| − | NOTE: Traps involving large quantities of water turning into steam are as effective at killing your | + | NOTE: Traps involving large quantities of water turning into steam are as effective at killing your {{l|framerate}} as they are {{l|goblins}}. Use with caution, and have the cut-off lever at the ready. |
===Drowning hall=== | ===Drowning hall=== | ||
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===Selective smiting tower=== | ===Selective smiting tower=== | ||
| − | This is a trap that can be built in discrete units. Each unit requires a lot of labor and protects only a small area, though in a dramatic manner. A wall of these around the map sharing a single massive water reservoir makes a very effective | + | This is a trap that can be built in discrete units. Each unit requires a lot of labor and protects only a small area, though in a dramatic manner. A wall of these around the map sharing a single massive water reservoir makes a very effective {{l|siege}} defense, as each tower component can be linked to a {{l|lever}} and used to wipe out a single invading squad at a time. Note: This may count as a {{l|stupid dwarf trick}}. |
| − | While a | + | While a {{l|pressure plate}} in the center of this trap can trigger it and drown hidden ambushers, such an arrangement is subject to double-activation and failure. A pressure plate that only triggers once will break and the system will be incapable of self-reloading. A lever is highly recommended. |
| − | Using a cross-hair pattern of walls, invaders are herded through the trap. Inside the fortress, Urist McLeverpuller does his job. | + | Using a cross-hair pattern of walls, invaders are herded through the trap. Inside the fortress, Urist McLeverpuller does his job. {{l|Floodgate}}s on the ground close, {{l|hatch}}es on the ceiling open, and drowning ensues. When all enemies are dead, the lever is pulled again. The hatches close and the floodgates open, allowing a rush of water and bodies to spill out. |
Schematics shown are for a stand-alone tower, though the upper level can be linked with many similar towers for a grid-like defensive system. | Schematics shown are for a stand-alone tower, though the upper level can be linked with many similar towers for a grid-like defensive system. | ||
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One method of creating a zone of constant slaughter is to link a pressure plate in your main dining hall or main hallway to a patch of menacing spikes or spears. As your dwarves/pets mill around conversing/mating, they will constantly trigger the spike system without regard to the consequences. | One method of creating a zone of constant slaughter is to link a pressure plate in your main dining hall or main hallway to a patch of menacing spikes or spears. As your dwarves/pets mill around conversing/mating, they will constantly trigger the spike system without regard to the consequences. | ||
| − | Variation: Drop goblins into a holding pit with various spike traps linked to your pressure plate artfully placed around the chamber. Watch as every dining hall | + | Variation: Drop goblins into a holding pit with various spike traps linked to your pressure plate artfully placed around the chamber. Watch as every dining hall {{l|party}} begins to be measured in goblin blood. |
===Chasm trap=== | ===Chasm trap=== | ||
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When building, you will need to {{l|construction|build}} a span of floor underneath, for the support, as bridges do not support constructions (''which is also why you want a bridge as the access, so it will not hold up the trap*)''. You will also need to have a floor tile between your floor and solid ground or wall while constructing, as the bridge alone will not work as a base, but you can remove it once the support is in place. | When building, you will need to {{l|construction|build}} a span of floor underneath, for the support, as bridges do not support constructions (''which is also why you want a bridge as the access, so it will not hold up the trap*)''. You will also need to have a floor tile between your floor and solid ground or wall while constructing, as the bridge alone will not work as a base, but you can remove it once the support is in place. | ||
| − | Because the outcome of this fairly complex trap can be easily obtained by just using a retractable bridge, it qualifies as a | + | Because the outcome of this fairly complex trap can be easily obtained by just using a retractable bridge, it qualifies as a {{l|stupid dwarf trick}}. |
===Land mines=== | ===Land mines=== | ||
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===Suicide booth=== | ===Suicide booth=== | ||
| − | Build a lever wherever you think is best, and nearly surround it with walls, leaving it open on one side. Install a {{l|trap component|menacing spike}} in the one open spot, and link that to the lever. Pull the lever once to lower the spike; The trap is set. Berserk dwarves or curious animals like | + | Build a lever wherever you think is best, and nearly surround it with walls, leaving it open on one side. Install a {{l|trap component|menacing spike}} in the one open spot, and link that to the lever. Pull the lever once to lower the spike; The trap is set. Berserk dwarves or curious animals like {{l|gremlins}} will freely pull it and solve your problems for you. This trap has some utility, and can be used for easily disposing of unwanted dwarves like {{l|Nobles}} by simply having them trip the {{l|lever}}. Should the spike fail to kill the creature, it will likely be severely wounded, and easy prey for your soldiers and/or war dogs. |
{{Military v0.31}} | {{Military v0.31}} | ||
Revision as of 13:48, 13 April 2010
| This article is about an older version of DF. |
- This page is one of several inter-related articles on the broader topic of defending your fortress and your dwarves. Trap design focuses on the theory and design of complex traps, mechanical systems and other automation for defending your fortress, and also on unusual uses of simple mechanic's Template:L.For a general overview of the threats that will challenge your fortress and things to consider when preparing a standard defense, see the Template:L. For tips on laying out your architecture to protect your military, see Template:L. For specific advice on how to get your soldiers prepared for any threat, see Template:L.
- For suggestions on disposing of nobles and other unwanted residents, see Template:L.
- For a basic overview of how the different machine parts work and work together, see Template:L.
- Editors & Contributors - Please see the discussion page before posting.
Introduction
Simple one-tile Template:Ls* are just that - they exist only on their own tile, trigger themselves when a target walks onto that one tile, and affect only that one tile. Complex traps and automation rely on linking Template:Ls, Template:Les, Template:Ls, Template:Ls and mechanic's traps to Template:Ls or Template:Ls, along with Template:L to provide the power to run some of the more diabolical designs. When the trigger is activated, it sends a Template:L to the linked device. That signal is not always as simple as "do it now", but it's specifically either to "open" or to "close". By manipulating what does what and when, and what follows from that, impressive results can be achieved.
- (* specifically, the Template:L, Template:L, and Template:L.)
- To fully understand how these component objects work individually (before combining them into diabolical and complex combinations), see those main articles.
Basic traps
These are the simple Template:Ls that are placed by a mechanic. They require one Template:L but do not require levers or triggers. They can be a quick, easy and brutally effective "first defense" for a fledgling fortress, but they can also be combined into key parts of more complex set ups. For tips on using these basic traps effectively, see the Trap Strategies section.
Stone fall trap
- This is the easiest trap to build, so you can easily build them in large numbers. Building lots of them is an easy way to earn experience for your Template:L, and add to the depth of your fort's defenses at the same time. Surrounding intersections and stairways is a good way of handling threats that make it inside the fortress, including berserk dwarves.
Weapon trap
- The gold standard of lethal traps. This is the only simple trap that works repeatedly without reloading. They do get jammed, however. View the trap with the items in room t mode, and if there's a corpse inside the trap, it's jammed. None of the weapons on a jammed trap will function. It may be wiser to have several weapon traps with fewer weapons, rather than a smaller number of ten-weapon traps.
- Using Template:Ls or other projectile weapons in weapon traps avoids the problem of jamming, but they must be kept loaded with Template:L. Mechanics will load them with any ammo that is not forbidden. They will load each until each type of weapon has ten rounds of ammo. Hammers seem to jam less than swords or axes, and spears seem to jam the most. Your dwarves will attempt to unjam traps unless otherwise forbidden.
Cage trap
- A very powerful type of trap. Maybe even too powerful - currently, even a wooden or glass Template:L can hold indefinitely any creature, even trolls and megabeasts. A cage trap never fails. Use cage traps as your outermost traps to catch the occasional wandering animal, or angry wounded Template:L or Template:L, or even Template:Ls. Caged animals and enemies will be safely brought to any animal stockpiles you have, but may escape later if you are not careful. For more information, see Template:L.
Linked traps
These traps require a trigger such as a Template:L or Template:L. They will require at least three Template:L, one for the trigger and two to create the link. The trigger can be located any distance from the trap, typically close for a pressure plate or far away for a lever.
For a system that repeatedly activates automatically and regularly regardless of enemies, see Template:L.
Menacing spikes
Menacing Template:Ls or upright spears appear on the basic mechanic's Trap menu, but must be activated remotely to pop out of the ground and impale anyone standing on that tile. Vast forests of these can make any area a killing field.
While upright spike defense systems never jam, they also do not discriminate. When activated, they will inflict piercing damage on whatever is standing on the tile, whether it be friend or foe.
Trap strategies
These are some basic tricks that can be used with most any trap design, basic or complex.
Bait animals
Enemies will hunt down and kill friendly tame animals wandering outside if they have nothing better to do. Put an expendable animal on a Template:L in some random spot outside, build a few columns around it to reduce the chance of them shooting it, and trap that area to hell and back. Also known as the "Tar Baby" strategy.
Note that this is a horrible method of getting rid of cats, as they will often adopt a dwarf who will then attempt to free the cat. This may lead to the unfortunate situation of Urist McCatlover getting skewered by an ambush party while on his way to free Mr. Baitykins.
Scattered traps
Another option for outside defenses is scattered traps. Most hostile forces will flee if they take enough casualties, whether deaths or cagings. This only works well if dwarves working outside are actually near the traps. A fisherdwarf on the opposite side of the map from a massive cluster of stonefall traps may as well have a large "KILL ME" sign on their back. If you like brute force methods, a wall of traps is a passive means to injure, kill or capture enemies who will happily walk right into them. (This can work so well that some players decline to use it, and prefer a more complex challenge.)
Trapping efficiently part 1
As the converse of building many traps everywhere, consider instead herding your enemies into a few traps. A cross-hair pattern of walls or impassable channels with an array of traps in the middle gap will increase the usage of each individual trap. This is particularly useful when capturing wildlife.
+++++║+++++ +++++║+++++ +++^^║^^+++ +++^^║^^+++ ═════^═════ +++^^║^^+++ +++^^║^^+++ +++++║+++++ +++++║+++++
Trapping efficiently part 2
If the path where you will place your traps has bends, expect the enemy to take the most direct path - it's not guaranteed, but they will tend to hug the inside of a corner, and rarely detour to a dead-end (represented by "x").
╔═════════ ║ ║xx ?? ║ ║x ??? ║???║ .???? ? = unpredictable path ║???║ .╔═════ ║ ??║ . ║ . = most likely path ║ .║☺ ║ ☺ = invader ║x . x║ ║xx xx║ x = unlikely detour ╚═══════╝
Once in a straight hall, anything is possible (represented by "?"), but placing your best (or first) traps on the inside path near "inside" corners (and de-emphasizing outside "dead-end" corners) is the best bet. If two invaders are side-by-side, they will wander, and random actions are always possible, but if you had to guess, this is the way to do it.
Crushing weight traps
Dropping the Hammer
Lowering Template:Ls on invaders will Template:L them into nothingness. Known as the 'Dwarven Atom Smasher', bridges will destroy most things with some notable exceptions including Template:Ls and Template:Ls, who will not only survive unscathed but also destroy the bridge.
Try replacing the side wall of a part of your main entrance with a drawbridge, big enough so it spans the whole hallway. To prevent enemies with the Template:L tag from wrecking it, you can dig a Template:L in front of it for protection while it's raised. Link the drawbridge to a Template:L, and whenever you feel like it activate the trap. This can be done with minimal effort and used to smash Template:Ls, unwanted Template:L, bothersome Template:L, or simply to destroy your garbage.
Intentional cave-in
Template:Ls can be linked to triggers. Building a section of floor that is deliberately held up only by a trapped support allows for an intentional Template:L.
- Invaders dropped into a pit can be wounded or killed.
- Dropping a floor directly onto any creature will instantly kill it, regardless of its size.
- The cave-in will also knock nearby invaders unconscious. This will stun them, and also make them susceptible to simple traps (even if normally immune).
- Cave-ins will not reveal invisible invaders, such as Template:Lers unless it kills them outright, in which case their bodies become visible.
The biggest drawback of this sort of trap is the "reload" process, which can be relatively time consuming. Have a drawbridge that can seal off the work area so your Template:Ls and Template:Ls can reconstruct the setup in peace.
Water traps
These traps drown or wash targets away. Carelessness can cause an entire fortress to flood and be lost. Use with caution.
Drown and burn
A flooding room trap combined with an unextinguishable burning Lignite bin. The water will evaporate on the bin's tile, causing the water from the surrounding tiles to move to it, which then get evaporated as well. The water will also push the invaders onto the fire, causing them to burn to death... in a flooding chamber.
NOTE: Traps involving large quantities of water turning into steam are as effective at killing your Template:L as they are Template:L. Use with caution, and have the cut-off lever at the ready.
Drowning hall
Level 0
░░░░░░░░░░░░░░░░░░░░░░░░░░░░ ░ - Wall ->++▼••••••••••••••••••▼++-> -> - Direction of traffic ->++▼••••••••••••••••••▼++-> ▼ - Down-Ramps (as visible from one level above = see Template:L) ->++▼••••••••••••••••••▼++-> + - Floor ░░░░░░░░░░░░░░░░░░░░░░░░░░░░ • - Open space
Level -1
░░░░░░XX░░░░░░░░XX░░░░░░ X - Inflow ░░▲++▼••▼++++++▼••▼++▲░░ ░░▲++▼••▼++++++▼••▼++▲░░ ▲ - Up-Ramps ░░▲++▼••▼++++++▼••▼++▲░░ ░░░░░░XX░░░░░░░░XX░░░░░░ ▼ - Down-Ramps
Level -2
░░░░░░xx░░░░░░░░xx░░░░░░ x - Outflow ░░░░░▲++▲░░░░░░▲++▲░░░░░ ░░░░░▲++▲░░░░░░▲++▲░░░░░ ░░░░░▲++▲░░░░░░▲++▲░░░░░ ░░░░░░xx░░░░░░░░xx░░░░░░
If enemies are in the middle of Level -1, open the inflow, then the water will first trap, and then drown them. If the pit is full, close the in- and open the outflow. You can automate this by using Template:Ls, or if you want to have more fun, replace the water with Template:L (which would require pressure plates and floodgates to be Template:L).
Selective smiting tower
This is a trap that can be built in discrete units. Each unit requires a lot of labor and protects only a small area, though in a dramatic manner. A wall of these around the map sharing a single massive water reservoir makes a very effective Template:L defense, as each tower component can be linked to a Template:L and used to wipe out a single invading squad at a time. Note: This may count as a Template:L.
While a Template:L in the center of this trap can trigger it and drown hidden ambushers, such an arrangement is subject to double-activation and failure. A pressure plate that only triggers once will break and the system will be incapable of self-reloading. A lever is highly recommended.
Using a cross-hair pattern of walls, invaders are herded through the trap. Inside the fortress, Urist McLeverpuller does his job. Template:Ls on the ground close, Template:Les on the ceiling open, and drowning ensues. When all enemies are dead, the lever is pulled again. The hatches close and the floodgates open, allowing a rush of water and bodies to spill out.
Schematics shown are for a stand-alone tower, though the upper level can be linked with many similar towers for a grid-like defensive system.
Level 0
░░X░░X░X░░X░░ ░ - Wall ░+++++░+++++░ + - Floor X+++++░+++++X X - Floodgate ░+++++░+++++░ H - Hatch ░+++++░+++++░ - - Water Reservior X+++++░+++++X ░░░░░░+░░░░░░ X+++++░+++++X ░+++++░+++++░ ░+++++░+++++░ X+++++░+++++X ░+++++░+++++░ ░░X░░X░X░░X░░
Level 1
░░░░░░░░░░░░░ ░-----------░ ░-H--H-H--H-░ ░-----------░ ░-----------░ ░-H-------H-░ ░-----------░ ░-H-------H-░ ░-----------░ ░-----------░ ░-H--H-H--H-░ ░-----------░ ░░░░░░░░░░░░░
Magma traps
These traps incinerate targets, or possibly encase them in obsidian. Magma does not play favorites - read up (again) on Template:L, and use with extreme caution.
Sealed Fate
Create an airlock using two bridges, two doors or whatever you like best. Make it a medium sized chamber, perhaps 10x10 or so. Channel out the floors around the rim, and rig up a system to pump magma into the room, or drop it from the roof. Enemies will quickly be destroyed, and with the magma in the channels, you can pump it out for future use or just leave it. The idea here is a re-useable magma trap; you can use this with a pressure plate, too. It also leaves behind any magma-proof items the invaders might have been carrying.
Variation: By placing magma-safe hatches on the ceiling and quickly activating and deactivating the trap, you can limit the use of magma. It doesn't take a lot of magma to set a goblin on fire: only 1/7 deep will do it, and using less magma means it will dry on its own. It does take a while for an enemy to burn to death, but what's better than spending the whole summer watching a room full of smoke and dying goblins?
Misc trap designs
By clever and creative use of various elements, it is possible to create impressive systems that fill a variety of functions.
Casual impalement
One method of creating a zone of constant slaughter is to link a pressure plate in your main dining hall or main hallway to a patch of menacing spikes or spears. As your dwarves/pets mill around conversing/mating, they will constantly trigger the spike system without regard to the consequences.
Variation: Drop goblins into a holding pit with various spike traps linked to your pressure plate artfully placed around the chamber. Watch as every dining hall Template:L begins to be measured in goblin blood.
Chasm trap
The easiest chasm trap is just a retractable bridge, very high up or over a very deep hole; instead of flinging invaders when raised, it just drops them.
A more complicated collapsing spiral trap can take out ten goblins at a time. When finished, it looks like this:
+++ ..........+++ .++++++++#+++ .+╔══════. # = retractable bridge .+║++++++. .+║+╔══╗+. + = floor .+║+║A+║+. .+║+╚═+║+. . = open space .+║++^+║+. .+╚════╝+. ^ = pressure plate .++++++++. .......... A = bait animal
The goblins are lured in by a Template:Led bait animal, and can't shoot it due to the surrounding walls. Just before they reach the bait, they trigger a pressure plate that retracts the bridge and collapses the support holding up the whole spiral. Goblins, bait animal, walls and all plummet into the chasm.
When building, you will need to Template:L a span of floor underneath, for the support, as bridges do not support constructions (which is also why you want a bridge as the access, so it will not hold up the trap*). You will also need to have a floor tile between your floor and solid ground or wall while constructing, as the bridge alone will not work as a base, but you can remove it once the support is in place.
Because the outcome of this fairly complex trap can be easily obtained by just using a retractable bridge, it qualifies as a Template:L.
Land mines
In any suitable open area which hasn't been dug out underneath, build a support and an adjacent multi-use pressure plate set to trigger on creatures (but not citizens), link them together, then build floor tiles above the support and pressure plate. When an enemy steps on the pressure plate, the game will pause and recenter the view with the announcement "A section of the cavern has collapsed!", at which point the enemy will be crushed and its companions will be stunned or knocked unconscious by the cloud of dust (though not necessarily revealed, in the case of an Template:L).
Pitfall trap
A long retracting bridge in your entrance tunnel, with the pressure plate right in front of the fortress doors. The expression on the face of the point-goblin who reaches them only to watch his comrades plunge to whatever gruesome fate you have prepared for them will be a mental picture to cherish.
You may also consider linking these bridges to levers for more control, just in case a goblin thief triggers the pressure plate while a caravan is on the bridge.
Degrinchinator
Water open to the sky in freezing biomes will freeze instantly, completely destroying anything caught in it. By digging a channel entrance to your fort and selectively allowing it to flood as invaders pass through, you can commit genocide with appalling efficiency. The only disadvantage to this trap is its size: because water freezes so quickly, each entry channel must have a source of non-freezing water right next to it.
Observe: http://mkv25.net/dfma/movie-231-degrinchinator
Suicide booth
Build a lever wherever you think is best, and nearly surround it with walls, leaving it open on one side. Install a Template:L in the one open spot, and link that to the lever. Pull the lever once to lower the spike; The trap is set. Berserk dwarves or curious animals like Template:L will freely pull it and solve your problems for you. This trap has some utility, and can be used for easily disposing of unwanted dwarves like Template:L by simply having them trip the Template:L. Should the spike fail to kill the creature, it will likely be severely wounded, and easy prey for your soldiers and/or war dogs.