If Isaac's speed is less than 1.5, passively increases his speed to 1.5.
Upon use, Isaac charges in the direction the pony is facing, giving invincibility during the charge and damaging enemies while also creating beams of light.
The beams of light are spaced randomly around the room and deal the same damage as those created by Crack the Sky.
The beams of light deal 4 times Isaac's damage, plus a flat 10 damage and trail behind Isaac as he charges.
The dash deals 40 flat contact damage to enemies.
The dash deals 4 times Isaac's damage, plus a flat 28 damage.
Isaac can dash through doors, which means that damage from Curse Room doors can be avoided.
Although the dash can persist between rooms, the beams of light only occur in the room it is used in.
While not time-based, invincibility from White Pony is otherwise identical to damage immunity granted by the invulnerability effect.
If White Pony is replaced by another activated item, Isaac will lose any passive benefits that it had granted.
Synergies
Book of Virtues: Creates white pony wisps on the middle ring that fire white tears with a 10% chance to fire Holy Light tears. The beams of light the wisps' tears make deal extra damage to enemies in a small area equal to 3x the wisps' tear damage.
Mars: Using White Pony after dashing lowers the dash cooldown to approximately 1 second.
Taurus / Thunder Thighs: The speed decreases from the items can lower Isaac's speed past 1.50 (making the new lower speed limits 1.20 and 1.10, respectively). Having both items can lower the minimum speed to 0.80.
3DS The icon of White Pony as seen on the lower 3DS screen.
Trivia
This item is a reference to the White Horse, one of the Four Horsemen of the Apocalypse described in the last book of the Bible. This is reinforced by the fact that the item is dropped by Conquest, which is a further reference to that passage of Christian theology.
The beams of light are spaced randomly around the room and deal the same damage as those created by 
Crack the Sky.
The beams of light deal 4 times Isaac's damage, plus a flat 10 damage and trail behind Isaac as he charges.
Curse Room doors can be avoided.
Conquest, as a starting item for 
Eden, by using 
Spindown Dice on 
Sacred Heart, or by using 
Death Certificate.
Bag of Crafting.
Book of Virtues: Creates white pony wisps on the middle ring that fire white tears with a 10% chance to fire 
Holy Light tears. The beams of light the wisps' tears make deal extra damage to enemies in a small area equal to 3x the wisps' tear damage.
Mars: Using White Pony after dashing lowers the dash cooldown to approximately 1 second.
Car Battery: No effect.
Taurus / 
Thunder Thighs: The speed decreases from the items can lower Isaac's speed past 1.50 (making the new lower speed limits 1.20 and 1.10, respectively). Having both items can lower the minimum speed to 0.80.
The Binding of Isaac: Rebirth
