It's called fake bird's eye. It's not a real perspective. It's basically two perspective combined. It's a pure top view (90°) combined with a pure front view (between 0° and 10° probably, depending on a few things). And the camera is in orthographic mode. Basically you won't be able to render a whole tileset at once. Arshes is a pretty good example of the fake perspective. His whole body is front view while his face looks like it's under an angle. His hair is the weirdest because you can see the stuff that is visible in frontview AND the part that is visible under an angle.