Walk
The walk is wobbly and not very smooth. Make the back leg come slower up and faster back down to the ground each step. His neck looks stiff so try to move his head up and down as he walks.
Punch
The legs shouldn't switch positions during the punch. The whole body should move forward (the stickman steps forward as he punches). Also don't bend his legs so much for such a small move forward, especially a punch.
Explosion
Very choppy, make the explosion slowly evolve and grow, and make small particles around it. Funny choice of colors. Make it longer (more frames) so that it is smoother.
Fishing
When the fish drags the cord, it should bend to the right, not left. When he's dragged into the water have less frames to make it faster.
Hope this helps. ^_^