What Binding of Isaac Item Gives This Mask
Solution 1:
If you mean the second screenshot, your "mask" is due to the Gnawed Leaf, as you can see this is the appearence:
That's the fifth item in your first screenshot.
This item is a reference to the "Tanuki suit" from Super Mario Bros 3, which also has a similar tail and the ability to turn into a statue.
Solution 2:
The item doing this was the Gnawed Leaf.
The Gnawed Leaf caused Isaac to turn to stone and become immune to all damage if he stays still and doesn't fire or use bombs/items for a second. The "white mask" was this effect.