At forty-two letters, "The Powerpuff Girls' Best Rainy Day Adventure Ever" is the longest episode title in the series.
In the rainy day episode, it is widely believed that some adult humour slipped through the net. When arguing about coming, Buttercup yells "Nobody makes me come!", which is followed by silence. There is also a scene where Blossom imitates Ms. Bellum by stuffing her stuffed animals in her dress to mimic Ms. Bellum's chest.
Although this episode premiered in 2000, it was produced in 1999 according to the credits.