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Place hazards and traps in your level

The same actors a throwable spawns when it lands can be dragged straight into a level. That gives you a fire pool in a corridor, a bed of nails in a doorway, a box that hurts anything walking through it, a box that pulls the AI towards it, and a tripwire rigged to an explosion.

They live in two folders:

  • Content/TheLastTemplate/Blueprints/Environments/Zones/
  • Content/TheLastTemplate/Blueprints/Environments/Traps/

The hazard actors at a glance

Actor What it does What sets it off
BP_ExplosionZone Damage in a radius, physics push, explosion effect and sound Itself, as soon as it starts
BP_MolotovZone A pool of fire that sets actors alight Itself, then anything entering it
BP_NailsZone A patch of shrapnel that damages what stands in it Anything entering it
BP_DamageZone A plain damage box, no effect, no sound Anything entering it
BP_NoiseZone Reports a noise the AI hears and comes to investigate Anything entering it
BP_Tripwire A wire across a gap that sets off an explosion The first actor to touch the wire

Every zone ships with its damage numbers at zero

Radius, Damage, Fire Damage, Fire Duration and Duration are all 0 on the class. That is on purpose: the throwables push their own numbers in when they spawn a zone, so the class defaults are never used. A zone you place by hand does nothing at all until you type values into it.

Values the shipped throwables push in, if you want a starting point:

Zone Comes from Numbers used
BP_ExplosionZone the grenade Radius 500, Damage 1000
BP_MolotovZone the molotov Radius 200, Fire Damage 5, Fire Duration 10
BP_NailsZone the nail bomb Radius 120, Damage 3, Duration 10

Place a zone

  1. Drag the actor from the Content Browser into your level.
  2. Select it and open the Details panel.
  3. Fill in the numbers below for that zone. Leaving them at 0 is the one mistake that makes a hazard look broken.
  4. Play.

If you want the same hazard many times, make a child Blueprint of the zone, set your numbers as its class defaults, and place that instead.

Explosions: BP_ExplosionZone

This one goes off on its own, the moment it starts. Placed in a level, it explodes when the level loads. That is what it is for: something else spawns it where and when the blast should happen. To arm a real trap, use BP_Tripwire below, or spawn the zone from your own Blueprint.

It applies its damage to everything inside Radius, pushes physics bodies away from the centre, plays NS_Explosion_Grenade and SC_Explosion, then removes itself when the effect has finished.

Field What it does Ships at
Radius How far the blast reaches, in centimetres 0
Damage Damage applied inside the radius 0
Impulse Strength How hard physics bodies are thrown 5000
Impulse Delay Short wait before that push, so it lands after the flash 0.15

Fire pools: BP_MolotovZone

When it starts, it traces down to find the floor it is standing over, sits itself Surface Offset above that surface, lights NS_Fire_MolotovBurst and scatters fire spots across Radius. Anything that walks into it and carries the CanBeFire actor tag starts burning.

The burning itself is not done by the zone. It adds a BP_FireComponent to the actor, and that component does the damage and the flames. See Make an actor catch fire for the tag and the one mesh setting that silently stops flames from appearing.

Field What it does Ships at
Radius How wide the pool spreads 0
Fire Damage Damage the fire does to what it catches 0
Fire Duration How long the fire lasts 0
Snap Down Range How far down it looks for a floor 1500
Snap Side Range How far sideways it looks for a wall or ledge 150
Surface Offset How far it lifts off the surface it found 3

The three Snap fields exist because a thrown bottle lands anywhere. Placing a pool by hand, you can leave them alone as long as there is floor under the actor.

Nail beds: BP_NailsZone

Plays NS_NailBomb_Shrapnel when it starts and damages anything that enters its box. After Duration seconds it removes itself, so a hand placed one is a timed patch, not a permanent floor trap. If you want it to stay, give Duration a large number.

Field What it does Ships at
Radius How wide the patch is 0
Damage Damage dealt to what enters it 0
Duration Seconds before the zone removes itself 0

A plain damage box: BP_DamageZone

No effect, no sound, no lifetime. It is built on the engine's Trigger Box, so you resize it with the brush handles like any other trigger volume, and it hurts whatever walks in. Use it for spikes you modelled yourself, for a pit floor, or for a scripted area you want to be dangerous without dressing it.

Field What it does Ships at
Damage Damage applied on entry 0

Damage goes through the normal path, so hit reactions, vitals and death all behave as usual. See How damage works.

A noise box: BP_NoiseZone

This one hurts nobody. When something enters it, it calls Make Noise with Loudness and Max Range and names the player as the source, so nearby AI hear it and come looking. It also plays Sound so you can hear that it fired.

Field What it does Ships at
Loudness How loud the reported noise is 1
Max Range How far the noise carries, in centimetres 1600
Sound Sound played when it fires SC_PerceptionNoise

Because the player is named as the source, the AI reacts as if the player had made the sound and walk to it. That is what makes it useful for pulling patrols off a route. For how hearing is tuned on the AI side, see Noise and distractions.

The tripwire: BP_Tripwire

BP_Tripwire is a spline. Drag it in, then drag its spline points to stretch the wire across a doorway or between two trees. It builds itself as you move the points: an anchor mesh at each end, Cable Mesh repeated along the spline, and a line of invisible box triggers laid out every Trigger Step with a thickness of Trigger Thickness.

The cable mesh has no collision. Those two numbers are the real hitbox, so if a character can step over your wire without setting it off, raise Trigger Thickness or lower Trigger Step.

The first actor to touch a box spawns a BP_ExplosionZone with your Explosion Radius and Explosion Damage, and flips Triggered so the wire can only go off once.

Field What it does Ships at
Cable Mesh The mesh repeated along the wire SM_Tripwire_Cable
Trigger Thickness How thick the invisible trigger boxes are, in centimetres 4
Trigger Step Spacing between trigger boxes along the wire 40
Explosion Radius Radius pushed into the explosion it spawns 500
Explosion Damage Damage pushed into the explosion it spawns 1000

Unlike the zones, the tripwire ships with usable numbers. Drop one in, stretch it, and it works.

Test targets: the two dummies

Two dummies ship, in Content/TheLastTemplate/Blueprints/Environments/. They show different things, and neither replaces the other.

BP_TrainingDummy is a torso on a stand, held by a physics constraint. It swings when you hit it and settles back. Its one field is Impulse Per Damage, at 200: every point of damage becomes that much impulse at the point that was hit.

It only answers to point damage, meaning a bullet or a melee trace that reports where it landed. An explosion applies damage without a hit point, so the training dummy takes the damage and does not swing. That is expected, not a bug.

BP_Dummy is a full character with a vitals system, a hit reaction manager and a health bar above its head. It bleeds, reacts, and dies with a ragdoll. Use it to check a weapon, a hit reaction or a hazard end to end. It has no fields of its own: tune it through its components, the same ones your own characters use. See Tune hit reactions.

Both carry the CanBeFire tag, so both are valid targets for a molotov or a fire pool.

Firing a hazard from your own Blueprint

Every zone reads its numbers the moment it starts, so setting them after the actor exists is too late. Set them on the spawn node instead.

  1. Add a Spawn Actor from Class node and pick the zone.
  2. Feed the transform where you want it.
  3. Fill the pins the node exposes for that zone.
  4. Set Instigator to whoever caused it, so the damage is credited to them.
Zone Pins on the spawn node
BP_ExplosionZone Radius, Damage
BP_MolotovZone Radius, Fire Damage, Fire Duration
BP_NailsZone Radius, Damage, Duration

This is exactly how the throwables do it. If your hazard should be attached to a throwable rather than to a Blueprint of yours, do not spawn it by hand: add a payload to the throwable's data asset instead, which is a list of entries with a radius, an amount and a duration.

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