Also affects maximum speed (may never exceed 2.0).
Running into enemies while at a high speed will deal 18 / 25 damage.
At least 0.85 Speed is required to be able to move quickly enough.
Moving at this speed also prevents contact damage.
Synergies
Serpent's Kiss: Allows Isaac to poison enemies without needing to take a hit, allowing for an impressive amount of Black Hearts to be collected.
Tainted Forgotten: Throwing the skeleton will deal 80 damage on contact.
Tainted Magdalene's hugs stack with Aries, dealing insane combined contact damage to enemies. This also makes T. Magdalene invulnerable at high speeds, whilst still generating a decent amount of red hearts.
Interactions
Isaac's Heart: The invulnerability does not extend to the heart.
Also affects maximum speed (may never exceed 2.0).
25 damage.
Serpent's Kiss: Allows Isaac to poison enemies without needing to take a hit, allowing for an impressive amount of 
Black Hearts to be collected.
Tainted Forgotten: Throwing the skeleton will deal 80 damage on contact.
Tainted Magdalene's hugs stack with Aries, dealing insane combined contact damage to enemies. This also makes T. Magdalene invulnerable at high speeds, whilst still generating a decent amount of red hearts.
Isaac's Heart: The invulnerability does not extend to the heart.
The Lamb's, and very similar to 
Curved Horn.
Zodiac Signs 
The Binding of Isaac: Rebirth
