When used, gives Isaac +0.4 speed and +3 damage and increases tears for 5 seconds, during which time he is restricted to using a jaw bone to damage enemies instead of his tears for 5 seconds, similarly to The Forgotten's bone club.
The jaw bone deals 3x Isaac's damage when swung and 1.5x Isaac's damage per tick when thrown (3x Isaac's damage per second).
The swung jaw bone reflects enemy shots.
The thrown jaw bone charges very quickly compared to the Forgotten's bone club, but as berserk only lasts five seconds, it uses a noticeable amount of the effect's limited duration to charge and throw the jaw bone.
While Berserking, Isaac's tear delay is multiplied by 2, then his tears fired per second is increased by 2. This will be a tears upgrade unless Isaac already has a lot of tears upgrades.
If playing as The Forgotten, the x2 tear delay modifier isn't applied, as he already has it.
Killing an enemy while "Berserking" increases Berserk's current duration by 1 second.
Killing an enemy also grants very brief invincibility, preventing damage from exploding enemies.
Isaac is unable to die while Berserk is active. He can be reduced to 0 hearts, but will not die until the effect ends.
This item charges when Isaac deals damage to enemies rather than by clearing rooms or picking up batteries. It requires a base total of 120 damage, and increases by 40 for every next floor.
The jaw bone has all the same synergies that The Forgotten's bone club does.
Mom's Knife: While the synergy between Mom's Knife and the Berserk state is identical to The Forgotten's melee attack, it is worth noting that the attack no longer deflects enemy shots.
The Lost / Tainted Lost: This can allow either variant of The Lost to survive being damaged if it happens while Berserk is active. Despite having no visible health bar, their health is normally set to half a soul heart. If they take damage while Berserk is active, they will not die if they are able to pick up a soul heart or half soul heart before the effect ends.
Book of Virtues: Spawns a pale wisp on the middle ring. The wisp has extra HP and does not shoot.
Car Battery: Duration is only extended if no enemies are killed during the first half, thus only providing a benefit against bosses that can't spawn enemies.
Sharp Plug: Isaac will take damage without gaining any charges.
The item's name, description, and effects are likely a reference to the Berserk power-up from the Doom franchise.
The phrase 'rip and tear' is frequently used throughout the Doom franchise, and was first used in the 1996 Doom comic after protagonist Doomguy picked up the Berserk power-up.
In addition, Isaac's inability to die during the effect could be a reference to the common joke of the main character of the Doom franchise being "literally too angry to die."
May be a reference to a character Chicken from Nuclear Throne who, unlike other characters in the game, wields a katana and upon losing all HP, instead of immediately dying, her head gets cut off and she can restore health in a short amount of time to stay alive before dying for good.
May also be a reference to the "Rage Beyond Death" ability with similar effects that Barbarians can gain in 5th edition Dungeons & Dragons, as the original Isaac characters were modeled after character classes from the game.
The jawbone Isaac uses is a Donkey's jawbone, which is a reference to a passage from the Book of Judges in which Samson kills one thousand Philistines using only the jawbone of a donkey.
It may also be a reference to the item Donkey's Jawbone from Antibirth that didn't make the cut for Repentance.
This event is also referred to by the pickup message for the Soul of Samson — "Slay a thousand".