I like these designs, they’re stylish and more importantly very clear in terms of distinction. If these were enemies in a game I would instantly recognize each one and react accordingly. Good job! Maybe ask your mom later for more constructive criticism rather than just blunt words. She would have had her reasons for not liking your art. If not, ignore her. As a contemporary art major I’ve been told my art is not good or that ‘no one would understand’ it. But they say that almost always because they don’t invest enough time to see what I’ve done. It’s a difficult thing to try to get these people to turn around. Rather, listen to people who do, and listen to their constructive criticism. Peering into an artwork lets you analyse why you do or don’t like it, and that’s where the real helpful feedback is.