Yokai of Sawaki Suushi and Toriyama Sekien
The above two Yokai related paintings were created by Sawaki Suushi and part of a series of picture scrolls titled "Hyakkai Zukkan" completed in 1737. Pink Tentacle has taken some of these paintings as shown at the Wikipedia Commons gallery and created an excellent article detailing the strange creatures from the scroll series. Check it out here.
Thanks to Paul for the link!
The following works are from Toriyama Sekien (1712 – 1788) "An 18th century scholar and ukiyo-e artist of Japanese folklore. He was the teacher of Utamaro, and, before taking up printmaking, a painter of the Kano school. Toriyama is most famous for his attempt to catalogue all species of yokai in the Hyakki Yakō series." Read more info related to the artist at this Wikipedia article. More of the illustrations from his series of Yokai can be found linked to these question marks and across the links on this Wikipedia page.