I still have no idea how to create a hydrus pet and I really want to make my cadogre Tumashevic hydrus ;/

could anyone tell me how exactly do i obtain the possibility to make my pet hydrus?

You need access to the Omen Islands, which you get by completing the Uncharted Land Map. Once you get that, just visit Merana and do her quest. :)

Thank you very much for your help!