Restrictive Tunnels
Classic villains for lower-level characters include goblins, kobolds, and derro. These notorious races, despite their wildly different physical appearances and abilities, have one thing in common: their size. As Small creatures, they gain a bonus to their Armor Class and on attack rolls, but the advantages of being small needn't stop there. Out in the open, large groups of organized goblins, kobolds, or derro can be a menace, but in their lairs they can be outright deadly simply because the size of a comfortable home for them is a major inconvenience for most of their enemies.
Low ceiling tunnels don't just come into play when fighting goblinoids. Natural caverns often constrict down to narrow passageways and low ceilings; these areas make natural haunts for smaller creatures such as chokers and darkmantles. The reverse is also true. A group of Medium PCs can gain substantial advantages by luring a dragon or a giant into narrow confines.
Restrictive tunnels can impede movement in two ways; they can have low ceilings, forcing tall creatures to crouch or even crawl. They can also have narrow widths, forcing larger creatures to squeeze through tight openings.
Movement in Cramped Spaces
Any creature fighting in a cramped space loses its Dexterity bonus (if any) to Armor Class. Beyond that, the following adjustments apply, depending upon the prevailing conditions.
Narrow or Low: An area that is smaller horizontally than a creature's space or smaller vertically than a creature's height falls into this category, so long as the constricted dimension is at least one-half the creature's space or height, respectively. A creature in such a space moves at half its normal speed because of the cramped conditions, and running and charging are impossible. The cramped creature takes a -2 circumstance penalty on attack rolls with light weapons and a -4 circumstance penalty on attack rolls with one-handed weapons. It cannot use two-handed weapons at all.
Narrow and Low: An area that is smaller in both the horizontal and vertical dimensions than the creature's space falls into this category, so long as each of the constricted dimensions is at least one-half the creature's space or height, respectively. A creature in these conditions moves at one-quarter normal speed and takes attack penalties equal to twice those indicated above.
Crawl-Navigable: An area less than one-half but at least one-quarter of the creature's height is crawl-navigable. The creature can move through each space by falling prone and crawling at a speed of 5 feet (1 square), but it must remove medium and heavy armor, backpacks, and other bulky equipment (although they can be dragged along behind). The normal penalties for being prone apply. The only ranged weapon a creature in a crawl-navigable space can use is a crossbow.
Awkward Space: An awkward space is narrower than narrow, lower than low, or smaller than crawl-navigable, but not quite a tight space. A creature in such a space can move 5 feet (1 square) with a DC 15 Escape Artist check. Fighting in an awkward space is possible only with light weapons, and the creature takes a -8 circumstance penalty on its attack rolls. The only ranged weapon a creature in an awkward space can use is a crossbow.
Tight Squeeze: A tight squeeze is an area larger than the creature's head but smaller than its shoulders, as described in the Escape Artist skill description. The creature can move 5 feet (1 square) with a DC 30 Escape Artist check. Fighting in a tight squeeze is impossible.
Weapons in Cramped Spaces
Some weapons are more suitable for use in limited space than others. Piercing weapons that jab rather than slice at an opponent are treated as one size category smaller than normal for the purpose of calculating the wielder's penalty on attack rolls. Such weapons include the dagger, short sword, rapier, spear (any type), and trident, but not the pick, scythe, gnome hooked hammer, or spiked chain.
Attacks with ranged weapons take penalties appropriate to the weapons' sizes in narrow or low conditions. Crossbows are the only ranged weapons usable in crawl-navigable and awkward spaces, but attacks made with them still take size-appropriate penalties.
Other Movement Modes
The rules for moving in cramped spaces above assume a creature using a land speed. Other movement modes are handled somewhat differently.
Burrowing: A creature that uses a burrow speed takes no penalties to movement or on attack rolls with light weapons in cramped spaces. Remember that a burrow speed allows movement through solid rock and stone only if the creature's description indicates such; otherwise, a creature can only burrow through loose earth.
Climbing: Climb speeds have no use in areas with low ceilings, but in narrow vertical spaces they are treated as if the creature were using a land speed. A Climb DC has a -10 penalty if the climber is in a cramped space.
Flying: A winged creature can use its fly speed without modification in low areas. A creature that flies without wings (using magic) can also use its fly speed in crawl-navigable areas. Fly speeds cannot be used in other cramped areas.
Swimming: In narrow or low flooded areas, a creature can swim at its full swim speed in low or crawl-navigable areas, and at half its swim speed in narrow or narrow and low areas.
