Shōkera

[1] In the Hyakkai Zukan, Gazu Hyakki Yagyō etc., they appear only in pictures with no explanatory text, so what kind of yōkai they are is a matter of speculation.

In folk religion, there is a custom called the "shōkera" in the Kōshin-Machi where, due to a belief in an insect called Three Corpses inside the body that on the Kōshin night would rise to the skies and report that person's crimes to the Ten-Tei (heavenly god) resulting in the Ten-Tei taking that person's life, people would spend the night without sleeping so that the Three Corpses would not leave the body on Kōshin night.

If I don't sleep" (しょうけらはわたとてまたか我宿へねぬぞたかぞねたかぞねぬば, "shōkera wa wata tote mata ka waga yado e nenuzotaka zo netaka zo nenuba") would ward off this harm, so from this, it can be seen that the shōkera of Kōshin-Machi is a yōkai that causes harm to people.

[3] The Gazu Hyakki Yagyō by Toriyama Sekien depicts a shōkera looking in through the skylight of a house's roof.

Yōkai-related literature starting in Shōwa and Heisei began to give the interpretation that this is surveillance to see whether people are following the rules of Kōshin-Machi day, and it is supposed that the shōkera would give a punishment by three fingers with sharp nails on those who break the rule.