Tension is, broadly speaking, how dangerous the game determines your current situation to be. This is automatically calculated based on a number of factors including number of enemies, strength of enemies, and current player status.
Several different in game mechanics work based on tension.
- Xom is more likely to act, and to act positively, when tension is high. The actions tend to more combat-relevant with higher tension.
- The Demonspawn's demonic guardian will only see fit to spawn if tension is high enough.
- When a vault warden seals doors, if closing a door would reduce tension too much (for example, because it separates you from a bunch of dangerous monsters behind it), that door will be left open. If an actor is standing on a door when a warden seals it, the actor will be pushed to the side that causes the higher tension.
- Cheibriados wrath has more dangerous effects (and as a result decrements faster) when tension is higher.
- The Singing Sword makes more noise with higher tension. At high tension, it changes its name to "Screaming Sword" and deals irresistible damage to all monsters in sight.
Tension is determined by looking at the surrounding monsters, and the player's current situation. For every monster in sight, the experience value is obtained, and then modified by the following factors. These modifications all stack with each other:
- Visible monsters unable to hurt the player add nothing to tension.
- Neutral or peaceful monsters add nothing to tension.
- Paralyzed, sleeping, or fleeing monsters do not add to tension.
- Monsters at below full HP have their contribution to tension proportionally reduced, so a monster at half HP will add/subtract half as much to tension.
- If tension is being called for a god-related effect, hostile monsters summoned by an angry god do not contribute to tension, with the logic being that gods do not care about minions they themselves sent.
- Friendly monsters subtract from tension instead of adding to it.
- God-summoned friendly monsters subtract twice as much from tension when considering divine effects (since the god is already helping you).
- Hostile monsters invisible to you have their contribution multiplied by 2.
- Hostile monsters that cannot see you have their contribution multiplied by 1/2.
- Confused or caught (in a net or web) monsters have their tension multiplied by 1/2.
- Slowed monsters have their contribution to tension multiplied by 2/3.
- Hasted monsters have their contribution to tension multiplied by 3/2.
- Mighty monsters have their contribution to tension multiplied by 5/4.
- Berserk monsters have their contribution to tension multiplied by 3/2. This increase is separate from and in addition to the increases due to Might and Haste.
These contributions to tension are then added up for every monster in range of the player (i.e. every monster in LOS, visible or not). Then, the tension is modified by the player's conditions as follows:
- If no monsters are nearby, it is set to 0.
- It is scaled to how injured you are. Specifically, it is multiplied by a factor of 2*Max_HP/(Current_HP + Max_HP), so tension is roughly doubled when you're almost dead.
- It is scaled down with your experience level. Specifically, it is divided by a factor of 1 + sqrt(Player's XP Points/30). This means at XL1 tension will be divided by 1, while at XL27 it will be divided by roughly 200. While the player will continue to accumulate experience points after XL27, these do not serve to further diminish tension, as the player isn't really getting any stronger.
- Tension is multiplied by 3/2 in the Abyss.
- Tension is multiplied by 10 if the player cannot act (i.e. is paralyzed through some means).
- Tension is multiplied by 2 if the player is confused.
- Tension is multiplied by 2 if the player is caught.
- Tension is multiplied by 3/2 if the player is slowed.
- Tension is multiplied by 2/3 if the player is hasted.