Introduction
Vibhavasu is a tortoise, cursed together with the elephant Supratika, a former sage-brother, to fight endlessly in the form of an elephant and a tortoise, until both were eaten in a single act by Garuda.
In the story
Vibhavasu shares fully in the story told of Supratika: the two were once sage brothers whose quarrelling led to a curse binding them to fight eternally as an elephant and a tortoise in a great lake, until Garuda, seeking food, seized and ate them both together, illustrating his tremendous size and strength. See the article on Supratika for the full account.