Numerous incidents of child abuse, including human experimentation on children. In a flashback, a character is implied to have been sexually abused as a child.
There are carnivorous, parasitic butterflies in chapters 54-56 and then chapters 111-112. 54/55 is the worst if you're like me and its parasites that bother you.
A sharpened object is driven into someone's eye. There are also several instances of characters crying blood. In later chapters, feather like things are coming out of characters' eyes
The main character's adoptive father dies before the series start. Lenalee and Komui's parents also died before the series start but this is only mentioned.
Possession is such a big part of this manga I can't warn you off a few specific chapters. The most graphic is the akuma wearing the bodies of their loved ones.
Clowns are common.
- Allen was raised by a clown and in battle he takes on the appearance of a jester/clown.
-The main antagonist looks like an evil clown, as do some of the akuma.