What is ushi oni?

Some articles on ushi, ushi oni:

Japanese Mythology In Popular Culture - Ushi-oni
... card game, there are three cards featuring ushi-oni "Ushi Oni" is a bull fiend with four octopus tentacles on its back, "Abare Ushioni" is a bull monster ... In the anime Karas, a bloodthirsty Ushi-Oni (voiced by Michael McConnohie) becomes a mechanized 'Mikura' concealing itself in the form of a police chief ... game Jade Empire, there is a two headed ushi-oni ...