This skill gives a Tzarakk bonuses to their physical stats which rise steadily when they are in combat and fall steadily when they are out of combat. Those who use it well can gain tremendous bonuses for long periods of time. Those who use it badly will surely die. Frequently. Ironically, this ‘reckless’ skill takes more strategizing than any other aspect of the guild. One using this frenzy needs to choose gear, healing methods, and their enemies carefully. It also is crucial to seek those hunting trophies which grant bonuses to this skill’s maximum training level.

The in game help reads:

Skill duration: 4.
Type of skill : neutral skill.
Affecting stats: Con.
It uses 21 endurance points.
Many of the cultists of Tzarakk still share the same primal instincts as wild
animals. In many ways the cultists do share similar traits and taste for
blood, like many beasts of the forest. The senses of the beastmasters are
always sharp and usually it's intrinsic for a beastmaster to act with a gut
feeling rather than to make a careful decision by putting one's mind into it.
To civilized people it's perfectly normal to use their brain, but the brutish
instincts of the beastmaster are often interpreted as barbaric and bestial,
although it's an essential survival mechanism. Many cultists of Tzarakk often
become threatened which may cause them to become infuriated and draw resources
they don't usually have. But it will usually make them less careful as well.
It's common to encounter a cultist who is overwhelmed by bestial frenzy when
they're in melee combat.