Agnes was the name of at least one of the heads of a "two-headed crocodile" that lived at the Gardens of Everlasting Summer.
She was pictured in an Alien Getaways brochure advertising the gardens that led the Thirteenth Doctor, Yasmin Khan, and Dan Lewis to investigate it and later cooperated with Yaz's enquiries about the gardens, although her other head disagreed with her about some of the specifics. (COMIC: The Everlasting Summer)