I must agree with Demotional. When I was growing up my favourite (Oh god. I feel so limited using a Pokemon example.) pokemon was undoubtably Hypno and Drowzee. Why? I still can't place a reason. But I never had one on my party at any given time because they scared me to no end. Dream eating tapir demons that stole your children?
..Sweet.
Anywhos, as for creatu, you really don't need to be that extreme. I'm thinking 'intimidating' animals rather than downright 'scary'. Wyrae and Ebilia are on that mark, definatly. Jaakus as well, (I always thought that they were really cute and cuddly until I found out that their mouths were stiched closed. Gross.) Maybe part of the 'menacing' factor is being gruesome. I always liked the fact that the Ebilia could 'dare' to show blood and flesh, with all the uproar that would cause. But really, there was a reasonable amount of blood in the freaking Lion King.
As for animals?
I still support the cl*censored*ic ideas of Elephants or Giraffes etc. But, as for m*censored*ive animals like that, I can see where there might be trouble with the 200px squared limitation. Maybe revert back to mythology, and make the creatures your own? Per example. You choose a Chimera, but you intend to base it off a goat. So, goat frame. But you can work with implanting feline and snake features into it, without actually having to explain what you did. (Achk. This sounded so much better in my head. D:)