Tiddalik is a Water-Holding Frog summoned by Tahlia. His name comes from the Aboriganal Dreamtime story of a frog that swallowed the world's water, then caused a flood when he was forced to laugh.
In the Books
He is introduced by Zerif as Tahlia's spirit animal.
In Venom, Shane views a painting depicting a frog with water in its mouth. This was probably alluding to Tahlia.
In Venture, he is mentioned by Tahlia, but it's still unknown if Tiddalik is dead or not.