Luison
Creature in Guaraní mythology
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The Luison (Luisõ in Guaraní; Luisón or Lobizón in Spanish) is one of the seven legendary beasts of Paraguay, and is the seventh and last son of Tau and Kerana. The myth is known also in Argentina and says that in a family with seven male children, the last child will become Luisón.[1]

Myth
In the original version of the myth, Luisón was the seventh and last child of Tau and Kerana, and thus was the most accursed. He appeared to be a giant dog, and was said to be extremely ugly, even horrendous looking.
The myth tells that the seventh son in a family will transform on his 13th birthday.[2]
Origin
The myth is widely present in roughly the same areas where the Maned wolf is present. Wolves do not occur naturally in South America, but when settlers arrived they brought their myths and legends, including lycantrophy. The maned wolf, a slender, wolf-like, stilted canid that moves with shambling steps, fitted the popular depiction of the werewolf and ultimately it was syncretized with local guarani myths.
In Santiago del Estero, Argentina, a similar description is now given to the Alma mula, originally a demonic spirit shaped like a mule.