Adds a chance to shoot tears in four cardinal directions, similar to Loki.
Notes
This item has a 1% chance to drop when defeating Loki.
The chance to shoot extra tears depends on the luck stat, and the formula used to determine the chance is:
At base luck (0), the chance is 12.5%, maxing out at 100% at 7 luck.
The chance to shoot extra tears depends on the luck stat and is based on this formula:
This means that the chance starts at 25% at 0 luck, minimizes at 0% at -5 luck, and maximizes at 100% at 15 luck.
Synergies
Mom's Eye: Each time Mom's Eye would activate, Loki's Horns activates instead. If Mom's Eye fails to activate, Loki's Horns' activation rate is still checked for afterwards.
Sprinkler: The sprinkler eye turns into four eyes and alternates shots between the cardinal and ordinal directions.
Technology 2: All additional tears are affected by the item but are replaced with Technology's lasers, effectively dealing 100% of Isaac's damage, and with 16 luck uses 100% of Technology 2's fire rate.
Tiny Planet: Effectively grants a great tear multiplier, as on item activation the extra tears will follow the trajectory given by the Tiny Planet.
Interactions
20/20/The Inner Eye/Mutant Spider: No effect on the tears fired in the other 3 directions. The chance to activate is checked per shot, not for each tear fired.
Dr. Fetus: Not recommended without immunity. Adds a chance to fire four bombs in cardinal directions.
Epic Fetus: Adds a chance to spawn four crosshairs in cardinal directions. Isaac controls one and the others will mirror the movement keeping their space.
Ipecac: Adds a chance to fire four explosive shots in cardinal directions. Caution is advised, though it is easier to avoid damage than Dr. Fetus.
The Ludovico Technique: Adds a chance for 4 piercing + spectral tears to be fired in cardinal directions from the main tear. This chance scales with luck and goes up to 100% at 20 Luck.
Mom's Knife: Adds four knifes on the cardinal directions around Isaac that can be rotated but all of them will be thrown when four tears would shoot with only Loki's Horns.
Monstro's Lung: Only one red tear will be fired in the other directions.
The laser rings will only fire forwards and backwards, with 2 stacked on top of each other in both directions, shooting at an angle will shoot the stacked rings at different angles.
Tractor Beam: Extra tears are not affected by Tractor Beam.
Loki.
This item has a 1% chance to drop when defeating 
The chance to shoot extra tears depends on the luck stat, and the formula used to determine the chance is:
The chance to shoot extra tears depends on the luck stat and is based on this formula:
Mom's Eye: Each time Mom's Eye would activate, Loki's Horns activates instead. If Mom's Eye fails to activate, Loki's Horns' activation rate is still checked for afterwards.
Eye of the Occult: Extra tears will fire in the same direction.
Sprinkler: The sprinkler eye turns into four eyes and alternates shots between the cardinal and ordinal directions.
Technology 2: All additional tears are affected by the item but are replaced with 
Technology's lasers, effectively dealing 100% of Isaac's damage, and with 16 luck uses 100% of Technology 2's fire rate.
Tiny Planet: Effectively grants a great tear multiplier, as on item activation the extra tears will follow the trajectory given by the Tiny Planet.
20/20/
The Inner Eye/
Mutant Spider: No effect on the tears fired in the other 3 directions. The chance to activate is checked per shot, not for each tear fired.
Dr. Fetus: Not recommended without immunity. Adds a chance to fire four bombs in cardinal directions.
Epic Fetus: Adds a chance to spawn four crosshairs in cardinal directions. Isaac controls one and the others will mirror the movement keeping their space.
Incubus: Not affected by Loki's Horns.
Ipecac: Adds a chance to fire four explosive shots in cardinal directions. Caution is advised, though it is easier to avoid damage than Dr. Fetus.
The Ludovico Technique: Adds a chance for 4 piercing + spectral tears to be fired in cardinal directions from the main tear. This chance scales with luck and goes up to 100% at 20 Luck.
Mom's Knife: Adds four knifes on the cardinal directions around Isaac that can be rotated but all of them will be thrown when four tears would shoot with only Loki's Horns.
Monstro's Lung: Only one red tear will be fired in the other directions.
Tech X: Overridden by Tech X.
Tractor Beam: Extra tears are not affected by Tractor Beam.