To me, the first issue is size. You've probably heard of the cube square law? As I understand it, for flight, there is a fifth power square law. Flight is hard, especially if you are massive.
The largest fliers at this point are some of the eagles. Huge wingspan, hollow bones for weight reduction, and mostly limited to soaring. The largest mammal fliers would be bats, which are cited as being the size of a small fox.
Thus, I doubt your creature could be much larger than a house cat.
It is probably mostly restricted to gliding and soaring.
If it can run, it can probably run faster than it can fly.
Indeed, that may be what it must do to get in the air.
I would expect this is normally used from the air.
Thus, it would sting downward and forward, between the hind legs.
The tail might well be carried high when on the ground, and thus resemble a scorpion.
The tail might also have some flight surfaces to it, giving it an unusual appearance.
It would need to be high energy.
Good candidates: meat, fruit/seeds, blood, milk. Probably only one, as each gets you a different jaw.
A jaw designed to tear flesh. Probably dog or cat like.
A jaw designed for crushing.
Probably lots of teeth, though maybe none and a digestive tract that does the work instead.
(Some birds do this, probably for weight reasons.)
The ability to induce bleeding, and suck on the blood.
This could get a human-like face.
The ability to suck on the milk.
Possibly no jaw to speak of at all.
This could easily get a human like face.
Personally, I like the idea of a milk drinker. If a large grazer has developed that both the females and the males lactate, and do so all the time, then the food source is good.
At this point, the sting could become a sedative or paralytic, used to obtain access to the milk without killing the beast.
This could develop into a mutually beneficial relationship, if the "manticore" acts as a high sentry for the herd, warning of approaching predators.
If such a relationship has gone far enough, the sting might also be used for protecting the herd.