Silhouettes are vaguely defined, I would encourage you to try to make them more precise. The human especially looks like some separate shapes displayed one next to the other.

See how the silhouettes are very thin and well defined? You should try to approach that, every pixel counts at low resolution

As far as the Medusa is concerned, I'd say the second convey well the spirit, and is less gimmicky than the third. But i'd try with fewer, more defined snakes to convey the feeling, here it really looks like hair, and I don't think it's what you want.
Keep up!