For all intents and purposes this is the unofficial prologue to Ojamajo Doremi. I'm not sure how Gomaato henshin'd into Onpu, though.
Gomaato is actually a girl [according to Toei Animation](http://www.toei-anim.co.jp/tv/crayon/chara/chara6.html), so her pronouns have been changed to reflect that—unfortunately, I only noticed this mistake after finishing the last episode with her in it. Her name is also romanized as 'Gomaato' and not 'Gomaata' (as it always has been) because I feel like the latter doesn't flow as smoothly in English. That aside, enjoy.
[SquareSubs] Yume no Crayon Oukoku - 11.mkv (152.3 MiB)