One non-mythological character ...
turned out to be decisive !
It's the very cute mechanical owl Bubo made by Hephaestus to assist Perseus,
in replacement for the owl Athena refused to hand over.
It retrieved the pouch containing Medusa's head Perseus had lost when
he fell in the sea.
Were it not for it, the Kraken would have snatched Andromeda.
I think Bubo is the apotheosis of all Ray Harryhausen's creations.