Ech Tened
The Ech Tened was a creature mentioned in the Epistil Isu, or Sunday letters, from Ireland. Its name means “fiery horse” and it was the third creature mentioned by these letters who punish those who do not keep the Lords Day holy. It was said that any who rode a horse on Sunday would be cursed to ride an Ech Tened in death as punishment.
Citations:
Bane, Theresa. Encyclopedia of Beasts and Monsters in Myth, Legend and Folklore. United States, McFarland, Incorporated, Publishers, 2016.