Trap

Version 0.25: This article may not be up to date for the latest stable release of Crawl.

Traps (represented by ^) are Dungeon features that harm the player or monsters who step on them. There are two types of traps: physical traps which are always revealed to the player, and exploration-triggered traps which are triggered by the player randomly during exploration. Most traps are magical in nature, but some vaults may also place mechanical ones.

Physical traps

Physical traps are always revealed to the player (but not necessarily to monsters). They can only be triggered by the player, or by monsters when they are in line of sight of the player. Flying creatures trigger traps in the same way as non-flying creatures.

There are six types of physical trap that generate randomly throughout the Dungeon and its branches:

• Teleport traps, which teleport anything that steps on the trap while in line of sight of the player to a different location on the current level. Destroyed when triggered.
• Alarm traps, which make an extremely loud noise and apply Sentinel's Mark to the player when the player or any monster steps on the trap. Destroyed when triggered.
• Shafts, which will cause monsters to fall 1-3 floors to a lower floor in the current branch when a monster steps on the shaft and fails a chance based on their intelligence and hit dice. Players can step on shafts safely, and pressing > will cause the player to fall through the shaft if they wish. Destroyed when triggered.
• Dispersal traps, which blink the player and all monsters in line of sight of the trap when the player or a monster steps on the trap. These traps are permanent.
• Zot traps, which cause random harmful effects to the player, possibly including teleporting them, creating dangerous summoned or durably summoned monsters, causing an explosion dealing damage to the player, or invoking dangerous levels of magical contamination, when the player or any monster steps on the trap while in line of sight of the player. When monsters step on the trap, there is only a chance for the player to be affected—this is indicated by the message "The power of Zot is invoked against you!". These traps are permanent.
• Webs, found most commonly in the Spider's Nest, can cause the player and non-spider monsters to become trapped and be given the Held status, halving their evasion and preventing melee and ranged combat. These traps are permanent, with the exception of those created by jumping spiders, which are temporary and destroyed when the player breaks or blinks out of them.

There are three more types of physical trap that can only be generated by vaults, most notably being seen in the hall of Zot on Zot:5 and the Tomb:

• Permanent teleport traps, which have the same effect as regular teleport traps but are not destroyed when triggered.
• Net traps, which fire a throwing net at the player, with to-hit dependent on the absolute depth of the trap, when the player or any monster steps on the trap while in line of sight of the player. These traps are triggered 2/3 of the time when stepped on by the player, and are destroyed when triggered.
• Pressure plates, which usually release monsters to surround the player when anything steps on the trap in line of sight of the player. The monsters released depend on the branch: in most branches, 8 redbacks will be released. In the Snake Pit, this is replaced by 8 black mambas and mana vipers, and in the Realm of Zot, this is replaced by a "klown kar"—3-8 Killer Klowns will be released. A few vaults have pressure plates that trigger different effects. These are always destroyed when triggered.

There are five more types of mechanical traps that can be found exclusively in the Ossuary. With the exception of blade traps, these traps all have a limited number of shots and are destroyed once their shots run out. The player has a 1/4 chance to trigger them when stepping on them, with the exception of blade traps, which are triggered 2/3 of the time. All mechanical traps deal more damage to the player than to monsters.

• Arrow traps: fire arrows, dealing 1-15 damage to the player, or 1-7 damage to monsters. They have 3-11 shots.
• Blade traps: swing a large blade, dealing 48-76 damage to the player, or 10-38 damage to monsters. They are never destroyed.
• Bolt traps: fire bolts, dealing 1-40 damage to the player, or 1-18 damage to monsters. They have 3-11 shots.
• Dart traps: fire poisoned darts, which may poison the target. They have 3-11 shots.
• Spear traps: fire spears, dealing 1-26 damage to the player, or 1-10 damage to monsters. They have 2-7 shots.

Exploration-triggered traps

When exploring new tiles that haven't been seen before, there is a depth-based chance that the player will trigger an exploration trap. There are three types of exploration traps that can be triggered:

• Alarm trap effect: the same as if the player stepped on an alarm trap; causes an extremely loud noise and marks the player. This effect cannot be triggered on D:1 or D:2.
• Shaft effect: the same as if the player voluntarily took a physical shaft; causes the player to fall 1-3 floors deeper in the branch with no immediate way to return to the higher floor. This effect cannot be triggered while standing on stairs or some other dungeon features, in the Tomb, Pandemonium, on the last floor of any branch, or on the second-last floor of all branches except the Dungeon, Lair, Orc and Depths, and you cannot be shafted from a higher floor into the last floor of any branch except the Dungeon, Lair, Orc or Depths.
• Teleport effect: causes you to be teleported to a random location on the current floor that is next to monsters, like the teleportitis mutation. This effect will fail to trigger if the game cannot find any such locations on the current floor.

Note that new tiles revealed immediately after a shaft or teleport effect won't trigger another trap effect, giving the player a bit of a break post-trap.

Worshippers of Ashenzari are completely immune to these effects.

Chance to trigger

The chance for each of the alarm trap, shaft and teleport traps to trigger when an exploration trap effect is rolled is 1/3 for each.

The chance for a given turn exploring new tiles is:

(number of floor tiles revealed on this turn / number of floor tiles on current level) * (1 + absdepth of current level/10) / 9

The chance for one or more exploration traps to trigger on a given level is therefore simply (1 + absdepth/10) / 9. This leads to the following chances of the game attempting to trigger one or more exploration-triggered traps on any given level:

Branch	Chance per floor
D:1-9	1/9
D:10-15	2/9
Lair	2/9
Orcish Mines	2/9
Elven Halls	2/9
Swamp/Shoals/Snake Pit/Spider Nest	2/9
Slime:1-2	2/9
Slime:3-5	3/9
Vaults	3/9
Depths	3/9
Crypt	3/9
Tomb	3/9
Pandemonium	3/9
Hell	3/9
Geh/Coc/Tar/Dis:1	3/9
Geh/Coc/Tar/Dis:2-7	4/9
Zot:1-2	3/9
Zot:3-5	4/9

The above chances are for the game to attempt to trap the player. Given that there are many situations when the shaft and teleport effects can fail, this does not accurately reflect the chance of actually being trapped on a given floor. Situations when a particular trap effect fails are not announced.

Obsolete Traps

Over the years, many traps have been removed from the game for various reasons.

• Needle traps were removed in 0.24.
• Shadow traps were added in 0.16 and removed in 0.17.
• Gas traps were removed in 0.13.
• Axe traps were removed in 0.11.

History

• Prior to 0.25, monsters couldn't spawn on top of traps. As a result, Animate Dead had no effect on corpses that were on tiles with webs. Also, scrolls of magic mapping didn't reveal traps.
• In 0.24, exploration trap effects will be made to only pick from eligible exploration effects.
• Dispersal traps were added in 0.23. Prior to 0.23, exploration-triggered traps did not exist, and physical traps were not always revealed to the player—instead, the player had an XL-based chance to detect physical traps and so would sometimes stumble into these traps. Worshippers of Ashenzari had an increased chance to detect these traps. Alarm and net traps did not affect the player when monsters stepped on the trap, and the trap layout in the hall of Zot in Zot:5 and the Tomb was very different.
• Prior to 0.16, flying players and monsters could avoid triggering traps. Shadow traps were added and trap disarming was removed in this version.
• Prior to 0.15, mechanical traps dropped ammunition and all teleport traps were permanent.
• Prior to 0.13, mechanical traps were randomly placed throughout every branch. Trap detection was based on the Traps skill.
• Prior to 0.12, Traps could be detected by searching (command s).
• Prior to 0.11, trap damage scaled with the floor's depth.