Every 40 seconds since activation or pickup, when the seconds on the timer hit 00, 20, or 40, while in a room with enemies, a shield triggers, nullifying all types of damage for 10 seconds.
This item is difficult to use for anyone with red health, as it is impossible to have no red hearts without removing all heart containers (such as through Devil deals). It is best used by characters that cannot gain red health at all, such as ???.
Characters can now deplete their red health fully through sources like Blood Donation Machines while having other hearts like Soul Hearts. As a result, this item is usable for a wider amount of characters, and has synergies with characters who prefer to have no red health (such as Eve).
Gnawed Leaf: If the player has no Red Hearts, they can stand still and wait for the shield to activate, allowing the player to deal damage without leaving invulnerability.
Black Hearts on pickup.
Keeper/ 
Tainted Keeper.
This item is difficult to use for anyone with red health, as it is impossible to have no red hearts without removing all heart containers (such as through Devil deals). It is best used by characters that cannot gain red health at all, such as 
???.
Characters can now deplete their red health fully through sources like 
Blood Donation Machines while having other hearts like 
Soul Hearts. As a result, this item is usable for a wider amount of characters, and has synergies with characters who prefer to have no red health (such as 
Eve).
Brittle Bones: The empty 
Bone Hearts will trigger Empty Vessel.
Gnawed Leaf: If the player has no Red Hearts, they can stand still and wait for the shield to activate, allowing the player to deal damage without leaving invulnerability.
The Lost's, but recolored.
Lazarus Unlocks 
Hush Unlocks 
The Binding of Isaac: Rebirth
