Berserker Manus

Berserker Manus is a unique Manus only obtainable by the Jotunn and the Vishaal. This unique Manus allows an individual of these species to enter a "Berserker Mode". When they use their Od circulating through their body their body mass doubles in size. This results in extreme increases in strength, durability, and zero loss in speed or quickness. A Vishaal who utilizes their Berserker Manus can reach strengths equal to a Jotunn in their prime, which is no small feat.
While this ability is highly respected and powerful it comes with a few strong drawbacks. The first is the form is very dangerous to maintain for extended periods of time as it results in the rapid increase of internal core temperatures as well as an extreme spike in the users' metabolism. In order to alleviate this members of these species eat large amounts of mostly meat and bone marrow, this gives them large amounts of proteins and fats the body can store for later. To alleviate the body temperature issues members of these species often wear very little armor, especially on the legs, chest, and head. On top of this Berserker form is used in short bursts of 3-5 minutes (8-10 minutes for members of the Vishaal as their bodies are much smaller cool more efficiently) but never over 5 (10) as at that point internal temperatures begin to reach around 105 degrees.
The final and most significant drawback of this form is that it is very taxing on the mind. The users must be highly disciplined in self-control and possess an iron will. These are the first things taught in their respective cultures. If one is lacking either of these or loses control of their emotions they go Berserk.
If they go Berserk this effectively this means they will continue and continue to fight with no self-preservation instincts until either neutralized or their internal temperature breaks 105 at which point the brain will usually disable the manus. However if they are particularly lost in their emotions or a sufficient amount of Vis enters the body, the brain won't be able to disable the manus. So they will continue to mindlessly fight until their brain literally boils in their skull driving them even more insane and finally killing them.