Here is a list of mythical creatures beginning with this letter and I am constantly gathering information from each continent and continually updating.
Alp-luachra (Irish)
In Celtic mythology, a Joint-eater, Just-halver or Alp-luachra (Ireland) is a type of fairy who sits invisibly and consumes half of their victim's food. When a person falls asleep by the side of a spring or stream, the Alp-luachra appears in the form of a newt and crawls down the person's mouth, feeding off the food that they had eaten.
In Robert Kirk's Secret Commonwealth of Fairies, this creature feeds not on the food itself, but on the "pith or quintessence" of the food. A man haunted by a joint-eater will never grow fat, because the pith or quintessence of the food is consumed by the fairy. People who consume newts are thought to be plagued in this way.