Greetings Canuck !
Well, in answer to your question : "How does Oskar come up with those designs?" . . . . .
I agree with John, this profile seems to indicate that Oskar should have no time to design puzzles! At least not in vast quantities. What an amazing guy. He seems to be one of those rare individuals who is successful at anything he or she puts their mind to.
I am a big fan of Hanayama and have most of the "Cast" series, but none of the newest stuff.