Tooth and Nail

Tooth and Nail is a passive item added in The Binding of Isaac: Repentance.

Effects[]

Every 6 seconds, Isaac turns to stone and sprouts spikes for 1 second. While Isaac is in this state, he is immune to damage and deals 40 contact damage.
- Isaac flashes white four times before turning to stone on the fourth flash. The first three flashes are accompanied by a "ticking" sound, the final one with the spike extension sound of a mimic chest.
- Unlike Gnawed Leaf, Isaac can still move and shoot tears.

Blood Donation Machines and Devil Beggars will still deal damage while Tooth and Nail is active.
With proper timing, Curse Rooms can be both entered and exited without taking damage.
When invincible, Spiked Chests/ Mimic Chests can be opened without taking damage.
When under the effects of the Paralysis pill Isaac cannot change into a statue.

Contact damage items work great with Tooth and Nail, such as Aries / Mom's Heels / The Virus for extra damage, Serpent's Kiss for Black Heart generation, Midas' Touch for coin generation etc.
Damocles: As Isaac is invincible 1/6th of the time, with some luck, Tooth and Nail may save him from the falling sword.
Kamikaze!: Allows usage without taking damage during invincibility.
The Lost can use this item to prevent additional damage from occurring after losing the Holy Mantle (for example, exiting a Curse Room after being hit), and it does not use up the Holy Mantle's 1-hit protection if it has not been lost.

PC 3T0E WTWQ (Treasure Room adjacent to spawn)

Bug!	If Tooth and Nail is lost while in the statue form (e.g. through losing its Lemegeton wisp), Isaac will indefinitely remain in the statue form until he leaves the room.

Bug!	Using an active item with no cooldown repeatedly ( Mom's Bracelet, Bag of Crafting, etc.) whilst in an invulnerable state will keep Isaac in that state.