Winnie the Pooh is an interesting example, because while the first book will be in the public domain, the second book and the Disney films will still be under copyright. So you'd be free to make a story or merchandise based on the original book Pooh, but you can't use the way he looks in the movie, nor can you use Tigger (who doesn't show up until the second book).

A similar thing happened with Sherlock Holmes, where there was a window where you could use Sherlock and his early cases, but you couldn't use details like Watson getting married because the later books were still protected (we might still be in that window, I don't know the publication dates off the top of my head).

It's an interesting question because it hasn't been litigated before!

If you make/sell a Winnie the Pooh bear and Disney sues they can't make the claim that they own the copyright to it (anymore). What they could claim is that it's a trademark of theirs but that protection doesn't necessarily trump the fact that WtP is public domain now. So the courts will have to decide if trademarks can overrule works derived from the pubic domain.

Legally speaking I don't think that makes any sense. It feels like it's the equivalent of trying to get a trademark on a common word or phrase which you can do (in theory) but it has to be severely limited in scope and trying to litigate it is basically wishful thinking.