Ego
Alright, this is Ego.
He is, quite literally, my ego.
I'm not exactly sure what kind of creature he is, or how exactly he works, all I know is that he is the personification of my ego.
At this current point in time, he's round about the size of a small dog, and I'm going to consider that his default size, seeing as he grows and shrinks according to how good I feel about myself and how much praise I am getting.
If he gets too big, he turns into a spiky monster with big long saber teeth and bat wings, so any praise should be tempered with constructive criticism. Please, I don't want to have to keep up with the food bills of a creature the size of a leopard (the biggest he can get).
He can get pretty small too, about six inches long at smallest. At that point, his wings are tiny useless nubbins and his fur is rather sparse and unkempt. His tail and his wings are the best indicator of his growth, as his tail will get longer and fluffier and his wings will grow to the point where he can actually fly. His horns also grow, curling like ram's horns.
And before you ask, yes, I know he looks kinda fox-like, and yes, his pupils are white. Don't ask me how or why, they just are. And, yes, I do realize his back foot looks weird.
This was a really quick doodle thing with some colors slapped on that I did on the computer cause I was bored and couldn't really think of anything to do and was feeling artistic.