Fires a powerful Brimstone beam in the four cardinal directions, much like The Fallen and Krampus shoot.
Has a 50% chance to rotate all beams around the player 90 degrees, similar to Krampus' second Brimstone attack.
Notes
Head of Krampus is one of two items that can drop by defeating Krampus. The other one is A Lump of Coal.
This is the only way to get this item normally.
Each beam deals 22 damage per tick, and they tick a total of 20 times, dealing a total of 440 damage per use.
Each beam deals 10 damage over 20 ticks, dealing a total of 200 damage per use.
Damaging enemies with the effect of this item as Guppy will spawn multiple Blue Flies.
By standing really close to large enemies such as bosses, it's possible to hit them with multiple beams at once, dealing significantly more damage than a single beam.
Synergies
Book of Virtues: Spawns red wisps in the middle ring. The wisps fire small Brimstone lasers in the cardinal directions when destroyed. The lasers deal the wisps' tear damage per tick, and can hit up to 20 times. BFFS! will not increase this damage, despite it scaling with the wisps' tear damage.
Car Battery: Doubles the damage the brimstone beams deal (for a total of 880 damage/ 400 damage per use). Doesn't double the brimstone beams' duration.
Brimstone beam in the four cardinal directions, much like 
The Fallen and 
Krampus shoot.
Has a 50% chance to rotate all beams around the player 90 degrees, similar to Krampus' second Brimstone attack.
A Lump of Coal.
Each beam deals 22 damage per tick, and they tick a total of 20 times, dealing a total of 440 damage per use.
Each beam deals 10 damage over 20 ticks, dealing a total of 200 damage per use.
Guppy will spawn multiple Blue Flies.
Book of Virtues: Spawns red wisps in the middle ring. The wisps fire small 
BFFS! will not increase this damage, despite it scaling with the wisps' tear damage.
Car Battery: Doubles the damage the brimstone beams deal (for a total of 
The Binding of Isaac: Rebirth
