Book of Virtues: Spawns red wisps in the middle ring that have higher health than average and shoot red tears.
Habit + Schoolbag: Damage from Blood Rights grants a point of charge to Isaac's other held active item.
Isaac's Heart: Blood Rights doesn't deal damage to Isaac, allowing repeated usage without penalty.
Shield/Invulnerability: Blood Rights can be used without taking damage for the duration of the shield or invulnerability. Invincibility frames from recently taking damage will not protect against this item's damage.
The Wafer: Reduces the damage dealt to Isaac to half a heart.
Bloody Lust / Bloody Gust: The Blood Rights damage counts for the raise of statistics of these objects.
Whore of Babylon: As Blood Rights takes Red Hearts before other heart types, it can be used to get the Whore of Babylon activation's condition easier.
3DS The icon of Blood Rights as seen on the lower 3DS screen.
Trivia
The item itself is a straight-edge razor.
"Blood Rights" is a term that means that the inherent has the right to certain things by way of heritage.
This item is possibly a reference to the 2002 film Gangs of New York, which deals heavily with themes of cultural obligation passed down through heritage; shortly before his own death, the main protagonist's father entrusts his son with his straight razor after having ritualistically cut himself with it, with the admonition that "The blood stays on the blade." The protagonist then hides the razor before being incarcerated and recovers it 16 years later, effectively making it his "inheritance".
The Necronomicon's effect, dealing 40 damage to all enemies in the room.
Red Hearts before other heart types.
This bypasses damage scaling.
Devil Room or 
Angel Room chances.
Curse Rooms without losing soul hearts.
The Lost or 
Tainted Lost kills The Lost, even if the protective effect from 
Holy Mantle is active.
A Missing Page / 
Missing Page 2: Deals an additional +40 damage. Effects stack together and with multiple copies.
The Book of Belial + 
Birthright as 
Judas / 
Dark Judas: Invokes the effect of 
Razor Blade along with its original effect.
Book of Virtues: Spawns red wisps in the middle ring that have higher health than average and shoot red tears.
Habit + 
Schoolbag: Damage from Blood Rights grants a point of charge to Isaac's other held active item.
Isaac's Heart: Blood Rights doesn't deal damage to Isaac, allowing repeated usage without penalty.
The Wafer: Reduces the damage dealt to Isaac to half a heart.
Bloody Lust / 
Bloody Gust: The Blood Rights damage counts for the raise of statistics of these objects.
Whore of Babylon: As Blood Rights takes 
Car Battery: No effect.
3DS The icon of Blood Rights as seen on the lower 3DS screen.
Samson Unlocks 
Satan Unlocks 
The Binding of Isaac: Rebirth
