Yuji Naka was one of the main designers for sonic. Hideo Yoshizawa was the designer for Klonoa. Seeing how both characters were made by different companies not affiliated with each other, the chances of any characters from either series being cross referenced is very unlikely. In my opinion, the artist here simply had a good hand at making the style of both characters work together. When it comes to fan art, you'd be surprised by what you can blend together to fit in one setting.

Huge props to the artist for using his Door to Phantomile design.