Edit
Deformed characters associated with the yukkuri shiteitte ne meme being mutilated, tortured or killed. Essentially a form of guro. Due to their resemblance to a manjuu, they are often shown to contain red bean paste instead of blood and viscera.
Images to which this tag would apply are prohibited on Danbooru.
However, images where yukkuri are mistreated with minimal detail (insufficient for the ryona or guro tag to be applied if they were human with human blood/organs) are permitted, particularly when the abuse is not the focus of the image or is presented in a slapstick context. Ask on the forums before uploading them if you are unsure.
Here are some examples of images that contain a permissible level of yukkuri mistreatment, and are allowed on Danbooru:
Do not tag images similar to these with yukkuri abuse.