What do you think the creature really looked like, and what made it so frightening???
Many headed snake-like creatures would be terrifying (at least off-screen in real life-just one snake slithering down unexpectedly over the wreath on your front door is enough). The legend of the Medusa is a familiar precedent (maybe the storyline writers had this in mind on DS, though keeping the Leviathan monster offscreen was a smart move, especially with the hokey props and effects of that era).
This sort of reminds of a Star Trek storyline involving aliens called the Kelvans who had assumed human form, but whose natural appearance according to Spock's mind meld was that of "immense beings, with many limbs that resemble tentacles."