EV3 T-Rex we build keeps toppling over on step
I built a walking machine when I was a kid several (cough) decades ago, and it had a similar problem. We finally figured out that what I had built was very front-heavy. Weight has to be balanced equally, forward and backward, over the "hips" of the creation. Pick up the creature by the top of the hips and see which way it swings. I solved the problem by adding a longer tail. You might also try putting the head up in a higher position or moving a battery case rearward.