Spawns a familiar that floats slowly around the room in a zig-zag pattern similar to The Peeper and shoots normal tears in the same direction as Isaac.
Each tear deals 3.5 damage.
Each tear deals Isaac's damage.
Spawns a familiar that follows Isaac and copies all of his tear modifiers/stats (like Incubus), with a 25% damage reduction. It fires randomly in the cardinal directions.
Notes
Unlike The Peeper, Cain's Other Eye does no contact damage.
Familiars that follow behind Isaac have a certain priority in how close their position is to him over other familiars, with Cain's Other Eye having 5th / 7th priority.
Interactions
Analog Stick: The familiar will fire in completely random directions, not locked to the cardinal ones.
Epic Fetus: Cain's Other Eye gains a crosshair and rocket similar to Isaac's but smaller. Caution is required, as the crosshair is erratic and will constantly shake, possibly making the rocket hit Isaac.
Eye of the Occult: The familiar's tears travel a very short distance in their original direction and can be controlled afterwards.
King Baby: Cain's Other Eye will attempt to fire directly at enemies but only when they are on the same side as the random direction it is firing in.
Mom's Knife: The familiar will constantly swing its knife, trying to point it in the random direction it is firing in. When the fire button is released, the knife will travel in whatever direction it is pointing at the moment (it can be any direction, not necessarily a cardinal one).
Cain's Eye, 
Evil Eye, or 
Glaucoma.
Spawns a familiar that floats slowly around the room in a zig-zag pattern similar to 
The Peeper and shoots normal tears in the same direction as Isaac.
Each tear deals 3.5 damage.
Each tear deals Isaac's damage.
Spawns a familiar that follows Isaac and copies all of his tear modifiers/stats (like 
Incubus), with a 25% damage reduction. It fires randomly in the cardinal directions.
5th / 
7th priority.
Analog Stick: The familiar will fire in completely random directions, not locked to the cardinal ones.
Epic Fetus: Cain's Other Eye gains a crosshair and rocket similar to Isaac's but smaller. Caution is required, as the crosshair is erratic and will constantly shake, possibly making the rocket hit Isaac.
Eye of the Occult: The familiar's tears travel a very short distance in their original direction and can be controlled afterwards.
King Baby: Cain's Other Eye will attempt to fire directly at enemies but only when they are on the same side as the random direction it is firing in.
Mom's Knife: The familiar will constantly swing its knife, trying to point it in the random direction it is firing in. When the fire button is released, the knife will travel in whatever direction it is pointing at the moment (it can be any direction, not necessarily a cardinal one).
Cain beneath his eyepatch.
The Forgotten, 
Tainted Forgotten, and other characters under the effects of 
Berserk!.
