First one is great
Second one is good, it looks like an athletic female. Might need a touch of tweaking, it's a bit androgynous. Maybe lightening the bangs to look less like eyebrows might do the trick. Or a mouth to help differentiate.
Third one, it's the body language that is off. If he's going to tackle you, add some knee bend and a bit of leaning forward. If it's more of a c'mon pose, or grappling, maybe the palms should be faced up or sideways, not down. The arms could also be at slightly different height to make it more natural of a pose.
It depends on what is going on. The design of the sprites themselves are all fine, depends on the context. If the context is more like an athletic ready stance, then the third's arms won't be out like that, would be more like the other two.
I think you're just getting a bit burned by the mirror tool.
Generally, nice work.