Hi! I'm glad you enjoyed it, the Turtle part was confusing to more people, I changed the game before you played it I think so that he tells you if you aren't strong enough and need to eat more, and the "T to flip" instruction was hidden until after you flip him over the first time. Before this update it was very confusing what you were supposed to do. So I'm happy you only had a problem finding where to use him.
All the puzzles can be solved without dying, but resetting the progress on death would have required a lot of extra work and would probably have made it a lot more frustrating to progress. Though there are some puzzles where you need to leave the area to either reset the enemy position or enter from another entry point to get everything. I was inspired a bit by the world design in legend of zelda in that you "come back here later", like you get to see the city walls and gate pretty early, you also get to eat a wayward sheep before getting into the human area and you see a farm with some farmland as well that you get back to later to destroy. The purpose was to create anticipation through teasing future content.