When Shaggy grabs a doughnut from his secret stash he grabs it from the icing side and when he is pulling it away the icing side flips to the bottom.
LEGO bricks cannot float.
When Fred is captured by the dolls, he is quickly tied up and carried off. However, seconds later he is seen freed and running away. This would be impossible because he was all tied up and nobody could have rescued him that quickly.