Cetacean Mimicry – The character has the form and/or characteristics of a cetacean. Cetaceans include whales and dolphins.
Giganto (Marvel) is more or less a whale that can walk (Marvel Pets Handbook #01).
Orca (DC) had Orca DNA inserted into her make up as part of a gene therapy treatment (Batman #579).
Razorfin Dolphin – Creature Collection II. Dark Menagerie
Armoured Gideon II – 2000 AD #828
Whale – TSR 2140A Monstrous Manual