Thanks! 
Well with an Empusa they'd be human enough to look at but with obvious differences (which makes up for their specialness) meaning they have to try harder to hide it. Could be since their 'awakening' they can't fully hide their eyes, ears, scales, fangs. So have to work hard to cover those by keeping their eyes downward/covered, their head covered with a hood or something, the afflicted body parts covered at all times, never smiling etc. Also I was thinking their emotions would play a huge part on their change whether they'd practiced or not. So any negative feelings could trigger a change and they'd have to quickly make a hasty exit before they're revealed. They'd likely be from the ice or desert kingdoms and I see them as a sorta odd job person, kill this or steal that kind of people. 

I was half contemplating a siren (merfolk are one of my favourite things to play but I am trying to steer away from my comfort zone) human enough though not fully able to ever hide themselves and don't really 'change' as such except when they get into 'hunting' mode. They'd have gills behind their ears or on their ribs meaning they'd forever have to be covered, webbed toes and fingers, meaning they'd have to wear gloves or long sleeves constantly and pale skin which would be hard to explain if they were from sunnier parts. Their 'hunting' mode would mean they get all black eyes, slight clawed fingertips and sharp shark like teeth, they'd be from the water kingdom the way I see them, used mainly for hunting/assassinations or bodyguards. 

As for my more normal idea I was thinking a Sand kingdom snake, possibly a cobra girl of some kind. Orphan of the state but not until she was 12 or so where she was then taken in by a low rung guard who for whatever reason decided he'd keep her. She got taught to fight and when her power awakened her guardian was silenced and she was hired as an infiltrator/assassin. She'd have a wholly desert like look, maybe a small 'tell' like slanted eyes or a more 'serpentine' manner. She can start her change to deliver poison kisses or venomous bites but that will be explained in much better detail in a cs. 

For the jungle cat I'm thinking 'wild tribe' as it were, perhaps some uncharted, or rarely visited forest/jungle where people like her fled to and live in a small sort of family group. Separated by some natural disaster or other and their more used to being their animals than humans, so perhaps she's captured by poachers, presented to one of the kings as a gift in her jungle cat form and during the night either breaks out and 'investigates' him only to be caught by a guard/ his queen and forced to flee or broken out by another Canavar who recognized what she was and somehow convinces her to turn into her human form. She'd be quite feral in mannerisms, more comfortable in her animal form but able ot communicate and function as human if she has too.