Hydras, fuckin Hydras when talk about mythological creatures. There's something badass about a giant serpent in which you cut on head off, two grow in it's place. I love that.
And Krakens....I love me a giant non-serpent like Sea Titan.
Demons. And not those pansy, shirtless, teenage-angst brooding "demons" who serve nothing more than to make a mockery of true evil; I'm talking the traditional demons. Giant, hellish, vile creatures who seek nothing more than evil for evil's sake. These things desire the souls of first-born children, the erosion of your sanity, your home, your power, your trust... only to backstab you whenever it suits their ends. They can supply you with your heart's desire, but always at a price. One that is always steep, and you can never avoid.