While in an uncleared room, 3-5 mime blocks appear at random places. Mime blocks prevent enemies and their projectiles from passing through, while allowing Isaac and his tears to pass freely.
If Isaac walks over a mime block, it will relocate to a random empty spot in the room.
Notes
Mime blocks can also block other entities, such as:
Mime blocks will not appear in the fights with Dogma or The Beast.
Mime blocks will relocate when in contact with Mother. This is to specifically prevent her from becoming stuck in her second phase when she charges across the screen.
Mime blocks are not considered real obstacles and are therefore unaffected by items such as D12 or Snow Globe.
Having multiple copies of Mime Degree will not create any additional mime blocks.
Interactions
Rubber Cement: Tears will bounce off of mime blocks.
Lost Fly: The fly can attach itself to mime blocks.
Tainted Lazarus: Mime blocks will only appear if the form holding the item enters the room; however, flipping to the other form will not remove any mime blocks currently in the room.
Tainted Jacob: Dark Esau cannot pass through mime blocks normally, but can do so when doing their charge attack.
China: China does not take damage when touching mime blocks.
Upon taking damage, Isaac will make no sound. Instead, a message will pop up, which reads either cries of pain: "ow!", "oof!", "ouch!"; or French profanities: "sacre bleu!", "mon Dieu!", "merde!".
Of the messages, there is a 0.1% chance of producing a very long string of text which is made up of Québécois profanities: "TABARNAK D'OSTI D'CALISSE DE SAINT SIBOUERE DE SACREMENT D'MAUDITE MARDE".
Instead of French profanities, Fiend with Mime Degree will instead create his own unique messages with censored swear words, exasperated shouts, or grawlixes: "F**k!", "S**t!", "D*mn!", "Cr*p!", "Gah!", "Grah!", "Bah!", "**** **** ***** ** *** *** !".
Bird's Eye, 
The Candle, 
Red Candle, 
Peppermint, and 
White Pepper (but not the ones made by 
Ghost Pepper).
Movable TNT barrels, including the one made by 
Mine Crafter.
D2.
Pet Peeve, 
Pet Rock, 
Blood Puppy (both the normal and angry forms), and 
Minions.
Dogma or 
The Beast.
Mother. This is to specifically prevent her from becoming stuck in her second phase when she charges across the screen.
D12 or 
Snow Globe.
Rubber Cement: Tears will bounce off of mime blocks.
Lost Fly: The fly can attach itself to mime blocks.
Tainted Lazarus: Mime blocks will only appear if the form holding the item enters the room; however, flipping to the other form will not remove any mime blocks currently in the room.
Tainted Jacob: 
Dark Esau cannot pass through mime blocks normally, but can do so when doing their charge attack.
China: China does not take damage when touching mime blocks.
Fiend with Mime Degree will instead create his own unique messages with censored swear words, exasperated shouts, or grawlixes: "F**k!", "S**t!", "D*mn!", "Cr*p!", "Gah!", "Grah!", "Bah!", "**** **** ***** ** *** *** !".
Shop item pool.
