Tips Solving Papouli's Puzzle Legitimately

[B.Z.B]

I used this strategy and it helped me solve it on my own for the extra puzzle piece
http://www.kopf.com.br/kaplof/how-to-solve-any-slide-puzzle-regardless-of-its-size/

Also referenced the completed pic https://i.imgur.com/ODSzVCZ.png to help