This skill is used by many non-boss torment creatures, generally when their health drops down to around 20%-40% of their maximum, although they have been observed to occasionally use it with health totals as high as 50%. When a foe uses it, that foe will stop moving, attacking, and using skills for 5 seconds.
The skill cannot be interrupted and knocking down the user doesn't interrupt it. Instead, the skill is considered "successful" the moment the creatures uses it, even though it doesn't take effect. However, they are still considered "activating a skill," so skills that cause a bonus effect if the target is activating a skill will still take effect.
The only way to prevent this skill from succeeding is to kill the monster attempting to use it. This is usually quite possible due to the double damage the creature takes and the fact that they only use this skill when low on health. However, since the skill lasts 5 seconds, and if the creature using this skill dies shortly after it, the duplicate will still be summoned, at which point, the summoned creature will appear a split second after the user is killed.
Lightbringer's Gaze is a good finisher for foes under Call to Torment. Depending on Lightbringer rank and the type of demon, a single Gaze deals 80-200 damage which is usually enough to finish off the damaged foe. Necromancers may also consider Necrosis, which does a similar spike of armor-ignoring damage.
The creature summoned by this ability is not considered to be part of the same party as the creature which summoned it. This means that it will simply linger in the area it was summoned and not follow any patrol paths often leaving it on its own and easy to kill. Similarly, aggroing the summoned creature will not aggro the party which summoned it and vice versa.
The creature summoned by this ability appears with full health and energy, and with this skill charged - NOT a duplicate of the summoning creature's current state.
If all the human players in a party are dead, the henchmen and heroes won't attack once a creature uses Call to the Torment, unless that creature is called. This can lead to many duplicates being created, until the henchmen are overwhelmed.
Signet of Sorrow, while not truly an effective counter to this skill, does help limit its effectiveness. Since the duplicate creature tends to stay put, it will often remain within range of the original creature's corpse, thus activating the skill's instant recharge feature. Thus the skill generates repeatable armor-ignoring damage to the summoned creature, with no energy cost.