As with other 'combat' dark gifts, Berserk required Kain's Rage Bar to be filled to a certain level (approx two-thirds filled) before it could be used. Once Kain had filled the Rage bar to the required level, Kain and his weapon would glow red indicating the ability was ready to be used. Once activated, Berserk consisted of a flurry of fast, "devastating" attacks, ending with the last strike and enemy falling away in slow motion. Berserk was essentially an upgrade of Kain's existing combat Dark Gift, Fury, which it effectively superseded. The animation of Kain's Berserk 'combo' varied depending upon the weapon he wielded whilst using it[BO2].
Berserk can be used earlier than intended by the use of Bonus mode. Notably early bosses will skip to the next phase of the battle when it is used (usage of the more advanced Combat Dark Gift Immolate generally finished the fight, cutting to the end cinematic)[BO2].
Originally the Berserk Dark Gift would have been the first 'combat' Dark Gift acquired by Kain (as Fury was a late addition to the development of Blood Omen 2). Berserk was also originally quite different in its use; being known as 'Speed ' and being more similar in nature to Slow Time artefacts from Blood Omen, slowing enemies movements (whilst increasing the speed of Kain 's.) This also better reflects Sebastian's use of the gift.
↑Berserk:"This allows Kain to perform a speed attack. Once Berserk has been selected from the Dark Gift menu and Kain enters autoface mode, he will begin to glow. Then, press the button to perform the Berserk attack in autoface mode" Crystal Dynamics. Blood Omen 2 manual. pg15 (Eidos Interactive). (2002) Download.
↑ 2.02.1"Berserk (gained by defeating Sebastian in Chapter 6)Unleashes a series of devastating blows." Prima Games. Prima's Official Strategy Guide to Blood Omen 2(2002).Page 2.ISBN 0-7615-3774-0
↑"Dark Gift:Berserk Like Fury, Berserk can only be used once you have filled your rage meter by blocking an opponent's attack. When Kain glows red, auto target your enemy and press the Dark Gift button. He'll unleash a flurry of blows with his weapon or claws, knocking the enemy to the ground in slow-motion." Prima Games. Prima's Official Strategy Guide to Blood Omen 2(2002).Page 54.ISBN 0-7615-3774-0
↑"When the traitor is dead, you will absorb his Dark Gift and take the Nexus Stone." Prima Games. Prima's Official Strategy Guide to Blood Omen 2(2002).Page 53.ISBN 0-7615-3774-0