Ok, this post is for those who might not know the mechanics of the Frenzied berserker
Why is he a risk? Why not just avoid going into a frenzy in the first place*? To avoid entering a frenzy in response to a provoking effect [Things that the deal damage], the character must make a successful Will save (DC 10 + points of damage taken since her last action) at the start of her next turn. [will is not a good save for the class BTW]
The frenzy ability boosts strength a fair amount [+6 upgrading later to +10], deals user 2 non lethal damage a round, stacks with rage and acts like rage [ lasts 3+ con mod, fatigued when frenzy ends, combo rage and frenzy and you get exhausted rather than fatigued when frenzy ends].
During a frenzy, the frenzied berserker must attack those she perceives as foes to the best of her ability. Should she run out of enemies before her frenzy expires, her rampage continues. She must then attack the nearest creature (determine randomly if several potential foes are equidistant)
and fight that opponent without regard to friendship, innocence, or health (the target 's or her own). BTW, the class’s second level ability is taking a 5’ step between attacks using cleave/great cleave so slicing into allies can happen very quickly.
Frenzy cannot be ended at the character’s choosing. To end it, the F.B. has to roll a DC 20 will save that can be attempted once a round as a free action.
As for why “Kill him in his sleep”? Because 4th level of FB the character cannot die while frenzying except by massive damage saves and other effects that outright kill the target. Most attempts at challenges and fair fights with a F.B. are greatsword assisted seppuku. Binding someone who can gain +10 to +14 to STR might not be too reliable either.
*The class’s real power comes from increasing power attack output, 3 for 1 with a 2 handed weapon at 5th level of the PRC up to 4 for 1 [with a 2 hander] at 10th.