Glad you liked the assets! About the mechanic I imagine you refer to the steps? If you walk to the left you get younger, right you get older. Each stage (age) has its pros and cons (well some more cons than others). Stage 1: Egg, can't move except right, breaks if falling (or bumped by pads). Stage 2: Little chick, you can crawl through tunnels, can't push rocks though. Stage 3: Adult, can push rocks but can't crawl through tunnels. Stage 4: Old chick, dies from falling/bumping from pads, can't push rocks, can't use tunnels or pads, basically you're close from dying.
If you meant explaining the reasoning behind it, we had a cutescene we had to delete (because Webgl didn't work out for our version of unity). The cutscene showcased an egg getting imbued by some sort of green potion giving powers, which allowed the chicken to get younger and older, we didn't have a story set in stone but a general direction to be sure!
I hope this all clears it out for you, if my answer was unfortunately too chaotic then I hope you enjoyed the game regardless! Thanks for reading :)