The Impact of Terrain on an Encounter: The Improvised Prison Example

Terrain can greatly alter the difficulty of an encounter.  Hide ranged attackers above a cliff and they are untouchable by melee attackers.  Bottleneck an incoming hoard into a 5 ft corridors, and the allies can defeat a 10x force.  More intriguing is how a simple reconfiguration of a hall in a building increases an easy encounter to a deadly one. In this post, I am going to look at this example in play in an improvised prison, taken from a recent game.

The improvised prison is roughly 20 x 20 square map made up of 5ft squares.  It consists of a single 10 ft entryway with 2 swinging 5 ft doors.  There are 12 cells around 3x3.  In the map as played, the cells are arranged in three rows.  One hallway accesses 1 row of cells; another hallway accesses 2 rows of cells.  Short corridors connect the halls to the main entryway.  All hallways and corridors are 10 ft wide.

The alternate way to build this map would be to build the hallway as either 1 big hallway that houses all of the cells, or a racetrack of hallways.  Each of these configurations drastically alter the dynamics of the fight.

In our scenario, there are 8 knights and one high cleric defending.  The cells are closed, locked, and the inhabitants are out of play.

In the one hallway case, all of the guards and the cleric are in the main hall.  The heroes attack through the front door.  8 guards attack in melee, but the hall chokes at 2 squares wide with an additional half square for the cells entries  The heroes have a caster and a ranged attacker behind two melee attackers.  The knights have 2 melee attackers in front with the cleric caster.  This direct 6 v 9 gets the knights killed pretty quickly, since 2 knights can't engage (melee only).  The cleric gets taken out in a couple of rounds after the knights' line is broken.  The single hallways is almost no challenge, because the party has more ranged attackers.

One Hallway heavily favors the Party

In the two hall case, he party rushes in and engages the couple of guards in the entryway.  The party scatters when squishy heroes back off to the two near hallways. 3 unseen knights run out and swarm the squishy heroes (rogues, bards, casters).  In 3v1, the squishies die in a round..  The party is flanked from the start.  If the heroes defeat the entryway guards, they must now split between the two hallways or stay flanked.  Splitting up puts the odds at 3v3 in each hall, if no heroes drop; the cleric floats where needed.  The fight is now a lot more balanced since the melee knights can engage.  The cleric takes the advantage at range.  The easy fight with one hall becomes a deadly fight with two hallways.

Two Hallways disrupt the flow of battle and favor the Defenders

In the acetrack hall case, the tactics are similar to the 2 hall case, except that for endgame.  In the end the split party wraps back around to flank the knights and cleric from both sides.  The final kills are a cake walk.  The encounter isn't hard and gets easier if the attackers rush in.

Racetrack Hall splits the Party, but ultimately results in the Defenders getting flanked.

4 key actions of the terrain increase encounter difficulty.  Terrain obscures the number and location of opposing force.  Terrain shapes the battle line between good guys and bad guys, effectively fixing the melee range ratio of good guys vs bad guys.  Terrain determines the split of the party.  Terrain sets flanking.

The encounter would play out very differently if there were more ranged attackers than melee attackers on the enemy side.  In this case, a longer single hallway would allow the enemies to pummel the oncoming heroes before they could reach melee range.  Ranged attackers inside the cells favor the defenders even more.

The other wild card in these scenarios is the ability for heroes and foes to alter the terrain.  A force wall, illusion, or other alteration to the terrain can reinforce or negate the terrain effects.  This can easily determine the winner.

This quick walk-through illustrates the impact of terrain on encounters.  Mind your terrain both when designing encounters and when playing them.  Use it often to keep your encounters interesting and your players sharp.