Butterfly Valley was originally a bright and cheerful show. Originally the first and most popular show created by Heykids studios, it was an animated cartoon about a pair of twins, Rose and Petunia, who were able to go to a world inhabited by fairies who turn into butterflies. This land was ruled by Princess Butterfly, a powerful princess. However, King Boogieman, the king of the Troll Kingdom, wished desperately to marry Princess Butterfly.
Here's where the controversy started. At trhe end of Season two, Princess Butterfly was engaged to a warlock named Frank, but it turned out he wanted to use Princess Butterfliy's powers to take over the world. The only way to prevent this was for Princess Butterfly to marry someone of royal blood: King Boogieman.
Many parents immediately saw King Boogieman's success in marrying the Princess as teaching children that evil can triumph, a very undesirable children's lesson. Despite this, he animators were able to curb the controversy by having King Boogieman visibly reform in season three. So for a while things were fine.
Then came season four.
During season three, Butterfly Valley's popularity declined because of competition from a show about a girl and some pirates, produced by the same company. The creators of Butterfly Valley mistakenly believed the rival show's popularity came from their dark tone, and made season four dark to try and compete, creating dark episodes with disturbing creatures and imagery.
That was their huge mistake. Many of the episodes in season four were banned. On top of that, Heykids had been creating some other controversial shows as well, and Butterfly Valley had been their least controversial show, and their biggest moneymaker.
Butterfly Valley's change in tone did the company in, as it's popularity plummetted. Realizing their mistake, they tried to return to their cheerful atmosphere in season five, but only two episodes were made of season five, because of lack of funding.
Now reruns are played on only one known station, and the show has been almost forgotten.
For details, one may look at the Butterfly Valley Wiki, which is currently under construction.