I read this book as a child which was in the early 1980s. I remember the ending the best so I’ll start there… a moon creature returns to the moon which appears as the moon should…empty with many craters, but then all the creature’s friends and family jump out of the craters to surprise him with a party. The rest of the story is a bit foggy but I remember that the moon creature was sad or disappointed for some reason and goes down to Earth by traveling on a moonbeam. He has an adventure possibly saving a unicorn from a scary witch that wants to take its magic horn. It wasn’t a long story, just a small story book