Daddy Long Legs' shadow follows Isaac and stomps on enemies for 20 damage per tick, with each stomp capable of hitting a single enemy twice for a total of 40 damage. The delay between stomps is approximately 4 seconds.
In a room with multiple enemies, Daddy Long Legs will prioritize on monsters with the most health first.
If all monsters are of the same type, the familiar will attack the closest enemy.
This item belongs to the Spider Baby set. Collecting three items from this set will transform Isaac into a humanoid spider.
Notes
The foot stays down for about 1 second, and enemies who wander into it will also take damage.
This item deals enough damage to kill most early enemies in one hit and is especially powerful against enemies with multiple segments like Larry Jr.
Synergies
BFFS! / Hive Mind: Increases the foot's size and doubles its damage. Both items cannot be stacked for an even stronger effect.
Box of Friends: Spawns an additional foot for the rest of the room.
Extension Cord: Bolts of electricity will arc between the shadow or the foot and Isaac and his familiars.
Gnawed Leaf: Allows Isaac to stay invincible while Daddy Longlegs clears the room, granting Isaac a slow but effective way of completely avoiding damage. This combination is especially useful as The Lost and Tainted Lost.
Spin to Win: Boosts the foot's damage while spinning.
The Twins: Has a chance to spawn an additional foot when entering a new room.
This item belongs to the 
Spider Baby set. Collecting three items from this set will transform Isaac into a humanoid spider.
Larry Jr.
BFFS! / 
Hive Mind: Increases the foot's size and doubles its damage. Both items cannot be stacked for an even stronger effect.
Box of Friends: Spawns an additional foot for the rest of the room.
Extension Cord: Bolts of electricity will arc between the shadow or the foot and Isaac and his familiars.
Gnawed Leaf: Allows Isaac to stay invincible while Daddy Longlegs clears the room, granting Isaac a slow but effective way of completely avoiding damage. This combination is especially useful as 
The Lost and 
Tainted Lost.
Spin to Win: Boosts the foot's damage while spinning.
The Twins: Has a chance to spawn an additional foot when entering a new room.
Duct Tape: No effect.
Forgotten Lullaby: No effect.
Sacrificial Altar: Daddy Longlegs cannot be sacrificed.
Spindown Dice: Turns into 
Polyphemus when rerolled.
Spider Items 
The Binding of Isaac: Rebirth
