Monsters: Tsurube Otoshi (Falling in Well Bucket)

"Nishioka no Tsurube-oroshi" (The Tsurube-Oroshi of Nishioka) from the Kokon Hyakumonogatari Hyōban written by Yamaoka Genrin, edited by Yamaoka Motoyoshi

Tsurube Otoshi (Falling in Well Bucket) is a yokai from Japan. It is a gigantic disembodied head of either a human, a tengu, or an oni and sometimes appears as fireball flames with facial features. Its size is the typical size of a human head to two meters in diameter. They live and spend most of their time in the tree tops preferring taller trees like pines, kayas, and other such conifers. The trees they live in are typically deep along paths in the forest and outside of towns where travelers are likely to be. The places they are known to be is the Wakayama Prefecture, the Kyoto Prefecture, the Shiga Prefecture, the Gifu Prefecture, and the Aichi Prefecture.

At night they wait in the treetops for unspecting creatures and travelers. When they need to eat they will quickly fall to the ground to trap their prey. This is how it got its name. They enjoy this kind of killing and let out a laugh as they hunt and eat their meal. Sometimes when they are not hungry they will come down and do the same crushing people to death for fun. Sometimes they don't use themselves, but large rocks or well buckets and enjoy the damage dealt. After they are done feeding and or having their fun they will slip back into the trees laughing and challenging others to pass underneath their tree.

Travelers are warned to not pass under the tall trees at night because the Tsurube Otoshi might get them. 

SOURCES:

Wikipedia

Yokai

Yokai Wiki