Threat

Version 0.17: This article may not be up to date for the latest stable release of Crawl.

The threat level of a monster is an indicator of how difficult or dangerous that monster is. This information is accessible through the monster list at the right side of the screen, or in the monster's descriptions. Ashenzari's monster detection, and Okawaru's piety gain also make use of this information. The game defines four tiers:

Threat level	Monster's name	Description
Trivial	Dark grey	"It looks harmless."
Easy	Light grey	"It looks easy."
Tough	Yellow	"It looks dangerous."
Nasty	Light red	"It looks extremely dangerous."

Formula

It is basically a ratio between the amount of experience points accumulated by the player and how many xp points a monster can provide.

Tension = Monster's XP points / ( 1 + sqrt(Player's XP points / 30))
If Tension is less than 1, Threat = Trivial
Else if Tension is less than 6, Threat = Easy
Else if Tension is less than 33, Threat = Tough
Else, Threat = Nasty