I like where this is headed! However, I think you could develop his character a little more, because right now he just looks like your average walking human-sized turtle. How about giving him some armor, boots? anything to give him some heroic/badass flair. You could give him an interesting armor-like plating to his shell, some leather straps, armbands... do some exploration.
As for the animations, I definitely think you could give him some more swagger in his walk. I imagine that since his legs are disproportionately small compared to the rest of his body, he has to rotate himself completely for each step - show his massive shell swinging left and right, give him some weight. You have a similar problem in the attack animations - you're trying to make the tween frames follow each other very smoothly, which does create a smooth animation but it doesn't portray energy buildup or weight very well. Think about the timing, when do you want the limbs moving slowly and faster?
For the attack animation, I would give a few more frames to the buildup and make him smash down in only 1-2 frames. For the fireball animation, he is very static. Play with the possibility of him recoiling while creating the fireball and surging forwards to release it. Good luck!
