I made every stage at hand, purple duck's AI is not really an AI, his AI is kind of complicated to explain how we did it, but we made the paths for him to run for each stage
I am a software engineering myself.
I hope you tried to do something like this: http://jceipek.com/Olin-Coding-Tutorials/pathing.html and also paying attention to the article in the very ending (steering) .
I think people use to choose a path finder algo for each difficult level, adapted to game engine and also other mechanics, like the duck grabbing.