Kill hole

Version 0.22: This article may not be up to date for the latest stable release of Crawl.

A kill hole (sometimes known as a murder hole) is a type of wall formation that only allows one monster into your line of sight at a time. This is an improvement over simply luring enemies into a corridor because most monsters will not do anything when they cannot see you; gnolls cannot reach you with polearms, orc priests cannot smite you, kobold demonologists won't summon any demons, necromancers won't shoot bolt spells past their zombies, etc.

Kill holes may occasionally form naturally, but most mentions of them refer to the creation of artificial kill holes with a formicid's digging ability or a wand of digging.

Examples

#########
####.####
###.#.###
##.###@## <--stand on
..#####g#    the @
##.###g##
###.#g###
####g####
####.####

This is an example of a naturally formed kill hole you might see in the Dungeon. Notably, it does provide monsters with a way to get behind you -- while the gnolls chasing you from the south are unlikely to find it unless there are a great many of them, any other creature attracted by noise or simply wandering may come around from the west.

.######
.Y+Y#..
.YY#@.# <--stand on
..#####    the @
#######

Another example, this time of something you might see in a semi-common layout of the Lair. Do note that this kill hole makes use of a closed door (the + in the middle of the yaks) -- when dealing with monsters that can open doors, this kill hole would not function correctly. Also, like the previous example, creatures may still show up from the east attack you from behind.

Creating a kill hole

To make your own kill hole, you'll need to either be a formicid or have a wand of digging and have a largish section of rock wall to work with. Ideally, the wall you're digging into won't have any open spaces close behind it that you might break into by accident, possibly attracting the attention of anything dangerous inside. The walls at the edges of the floor are usually perfect for this (though if you're too close to the edge of the floor, you might run into the indestructible border walls), but you can make do with digging into a large pillar or the like.

A proper kill hole (one which only ever allows one enemy into your LOS) ideally looks like this:

####
.#@#
#.##
####

Formicids, with their ability to dig into walls one space at a time, can easily make winding tunnels where each individual tile is its own kill hole. Of course, other characters will only have a wand of digging at their disposal and won't be able to make anything nearly so precise; they can, however, make a perfectly functional kill hole with only a little extra empty space behind them. To begin, find a suitable patch of rock wall:

#############
.############
..###########
...##########
..@##########
...*#########<-- Dig pointing at
...##########    the asterisk
...##########
..###########
.############
#############

Now, take a couple steps into your new tunnel, then dig diagonally in the other direction:

#############
.############
..###########
...##########
...##########
....#*#######<-- Dig pointing at
...#@########    the asterisk
...##.#######
..####.######
.######.#####
########.####

Stand just inside the entrance to the second tunnel, and congratulations, you've got a kill hole!

##########.##
.########.###
..######.####
...####.#####
...###.######
....#@#######
...#.########
...##.#######
..####.######
.######.#####
########.####

The only downside to making a kill hole with a wand of digging is if any creatures you're fighting have the ability to blink. They may end up blinking into the empty space behind you, leaving the path clear for a second enemy to get at you.

Tips & Tricks

• Kill holes are best used when you know there are monsters nearby with dangerous abilities that rely on sight; dangerous summons, powerful ranged attacks/spells, Smiting, Damnation, and Torment are all good examples. If you alert a number of monsters with these abilities while exploring, you may wish to retreat to a suitable kill hole (or quickly build one yourself, if there isn't one nearby).
  • If you know there is a vault with monsters of this sort on the current level, you may wish to preemptively build a kill hole and retreat there after attracting the attention of creatures in the vault. Particularly good places to do this include Orc:2, the ends of the various Lair rune branches, and Zot:5. (Elf:3 used to be a good place to do this before deep elf elementalists were introduced; see below.)
• Kill holes prevent monsters from seeing you, but they also prevent you from seeing monsters. Try to pay attention to any messages that mention noises coming from behind whatever you're fighting, as that might announce the presence of a monster you hadn't known about when you retreated. Formicids have yet another advantage in their ability to sense creatures with their antennae.
• Always make sure you have an escape plan. Even with the advantage of facing your enemies one at a time, you may get unlucky and end up overwhelmed and backed into a corner. Alternatively, something far more dangerous than the enemies you were fighting might be attracted by the noise and suddenly appear with little to no warning. A scroll of teleportation is perfect for escaping -- just be sure to leave time for it to kick in.
• Some monsters (like deep troll earth mages or cacodemons) have a Dig spell of their own. They will happily break you out of your carefully prepared bunker and open paths for their allies to swarm you. Deep elf elementalists are even worse, as their Awaken Earth spell turns nearby walls into hostile earth elementals; don't bother with a kill hole on Elf:3.

History

• Prior to 0.22, Lee's Rapid Deconstruction could destroy walls, possibly enabling the creation of kill holes in stone, crystal, or metal structures.
• Prior to 0.20, wands of disintegration could be used to remove one tile of rock wall at a time, giving all characters access to formicid-level precision in making kill holes.
• Prior to 0.14, players had access to the Dig spell.